Custom Title with BBcode

[MC2919]

I let my smods using the custom title, so they can change their titles anytime thay want through UserCP. However, their titles turn out to be in normal text. I would like to have custom title appears in black and bold or any pre-defined form I set without going to ACP and change the title per my smod's request.

I'm thinking of using a profile field and put it in the postbit template, but I don't know how to make it appears only to one group in UserCP, so other groups can't abuse the field to get a custom title.

Anyone please help me, thank you.