I think it's a great idea. It's a representation of who you are. I have no tattoos, but have been thinking over the last six months about how badly I want one. If only my wife was on board.
I'd like something to represent me and this particular time in my life. If "sly" is a representation of you, a reminder of who you are, whatever, than it's a great idea for a tat. Do it man! Post a pic when it's done.