so just thinking out loud;
Some of the things that do fit:
Mandalorians wear *distinctive* armor. It is the distinctive part that is important. It tells the Galactic public that they are not dealing with some loner bad shebs...they are dealing with a bad shebs from a culture of bad-shebs'e who have each others back; like family. The armor is a veiled threat, even before the mandalorian says a single word. It projects.
Outlaw Motorcycle clubs have their 'colours' aka their 'Kutte' aka 'cut'. Which is the vest with the distinctive patches; one is the identity image of the club. The top rocker is the name of the club. The bottom rocker is the location of that chapter aka charter. This garment, when worn, serves the same purpose as a Mandalorians armor. (aside from the actual armor application.)
"Mandalorians believe confrontation is required for growth, on the personal as well as the cultural level. War is the Mandalorian way of life."
―Jedi Master Gnost-Dural
Outlaw MC members have to be prepared to take violent action. They take pride in not living according to society's standards. When it was once said that 99% of motorcycle enthusiasts are peacful law-abiding citizens, then the Outlaw Motorcycle Clubs took pride in saying that they are the other 1%. This is why many wear the 1% patch and they are often called one-percenters.
Mandalorian culture is centered around family, a clan. It can be blood relatives or adoptive...it makes no difference, as long as they choose to be a part of the lifestyle. There are many clans, but a mandalorian will help a stranger mandalorian because they share the same culture.
Ditto for an MC. The members of their charter are the family, closer even than blood. Right after that is ties of loyalty to their blood family and that of the other patched members of their charter.
They will come to the aid of any other member of the same club, even if they are in another charter, which might be in another state or even country.
Mandalorians come originally from a warrior culture of military profession. Mandalorians have a history of being nomadic. They may set up settlements, but it is in their culture that they never expect to stay there permanently. They are also considered outsiders in mainstream galactic society, for they put their own values of freedom above Republic or Imperial law.
Bikers clubs grew out of soldiers coming back from World War II, who missed the danger and excitement, and especially the camaraderie of their brothers in arms. Their biker culture centered around the use of cruiser motorcycles, particularly Harley-Davidsons and choppers, and a set of ideals which celebrate freedom, nonconformity to mainstream culture and loyalty to the biker group. Biker chapters can settle down in areas, yet still frequently go on the road. Some chapters never settle down; instead of having a location on their colours they are 'Nomads'.
Outlaw bikers prize their sub-culture above all else. While organized crime seeks to make money, and break the law so that they can make more money, MCs see money as only the means to continue to live the biker way of life, and will make money legitimately or criminally as the means are available.
Mandalorians will hire themselves out as soldiers, enforcers, bounty hunters, guards and assassins because their skills are in demand and their reputations for skill and ability to conduct violence are well known.
Bikers will hire themselves out as enforcers, bounty hunters, guards and assassins...and many have served as legitimate soldiers; all because of their reputations for violence are well known.
Mandalorians have markings of honour, such as Jaig Eyes; symbols to other Mandalorians of accomplishment.
MCs have patches that can be worn that will have meaning to other members; such as various pilot-type wings; the true meanings of these patches can never be known as the club does not reveal the meaning to outsiders; 'Men of Mayhem' patch, for example, is commonly believed to be awarded to one who has inflicted grievous violence on behalf of the club.
Women in Mandalorian culture are treated as equals and are trained to be warriors alongside the men. You cannot marry a mandalorian without becoming part of the culture.
Women in Biker culture have typically been seen as subservient and considered property. This is true however only for hang-arounds who allow themselves to be treated as such, like groupies to a rock band. They partners of full patch members are considered part of the culture. They are not truly equal in that they don't ride and aren't a part of the democratic running of the chapter, but they hold a lot of power over their men, and are equally devoted to the club and its lifestyle.
"We did it. We showed them we are real women dealing with real men. I'd much prefer to be living with an OMC member than some dork who is a pawn in the system" stated one woman who felt she and her peers had "set the record straight" -wiki
'Female partners, sisters, mothers, aunties and children, particularly female children, are often the central meaning of a club member's life. In the vast majority of cases, the children and partners of the members are the reason for their existence as men and their job, as a man, is to protect the women and children. Their women are fiercely proud to be partners of outlaw motorcycle club members.' -wiki.
Mandalorians must live by their code, the Resol'nare, the six actions, in order to be considered part of the culture;
They consisted of wearing armor, speaking the language, defending yourself and your family, raising your children as Mandalorians, contributing to the clan's welfare, and when called upon by the Mand'alor, rallying to his cause.
MC members have their own code, as defined by each charter, but the tenets of the Resol'nare are there; albeit MCs have no official language; and the Mand'alor would be the MC President of the original chapter. And Presidents can and do call upon the members of other charters to go to 'war' when required.
A mandalorian without armor is not truly a mandalorian and cannot fully partake of the culture. Just as in most MCs, a member who cannot ride a motorcycle has his membership status reduced. You can't be a rank or position if you can't ride due to medical reasons, for example.