I think we had a similar question asked a while ago but in the form of tattoos being used, but they aren't apart from Yakuzas and other organised crime gangs. The thing with tattoos and other symbols like that isn't too clever as it proves you associate with other known criminals. The government could then use it against you to prove a conspirocy case that you're part of an organised crime group. The way wiseguys know who other wiseguys are, are by the way they're introduced. "This is a friend of ours"...etc. Even from another Family it could be used for. But they'll also never say which Family they're with. Usually they'll say who they work for, either Capo or Boss. "This is a friend of ours, he's with Paulie from Mulberry Street" ...etc.

Wiseguys, as tradition are supposed to look sharp. Look powerfull in there suits but there's no dress code really. As Saladbar once said to me, the allussion of power is power and it's pretty true. But dressing in such a way is a give away to law enforcment officials, some wiseguys prefer to dress down, to stay underground and low key. Sammy the Bull was known for this in contrast to John Gotti's dapper look. He did quite well for himself until Gotti ruined it all.