I wouldn't use isin if I were you, it's too great a chance to get your script compromised by another nickname who shares part of yours.
Let's say > PyThOn is the owner nickname and someone named > GrumpyPyThOn996 will be able to command and take charge of the client running the code.
I would use
if ($wildsite == $address($me,2)) {
if you run two mIRC using the same host
Or
if ($wildsite == *!*@YourHostHere) {
To specify your own.