If you press A when you're looking at your trainer card (at least on D/P/Pt I know) It's say when your hall of fame debut was, how many times you've linked, the no. of link battles won and lost, how many link trades you've had, and if you chose to do it, a signature. So. Just post what on the back of your trainer card. Here's mine:
Hall of fame debut: Apr. 18, 2009 at 0:01
Times linked: 110
Link battles: W - 26 L - 5
Link trades: 59 (I guess it counts every time you go to the GTS)
And my signature is The initials P. M. with a curl at the end of the M for Prison Mike.