Sorry for this newbie question.... I read some thread and learned that I can change the email signature (mine's still the default BB signature it came with) by using the Desktop Software. But the software doesn't seem to be compatible with macs (OS X).

How can I change or delete my email signature? Thanks.

You change your email sig through your your Blackberry account. Ya know, where you registered your PIN/IMEI and all that.

Yep. And with BIS 2.0 you can have a different signature for each account.
An even more versatile option is to get rid of the signatures on BIS and create autotext signatures on your Blackberry.

If you're a Cingular customer, go here: https://bis.na.blackberry.com/html?brand=mycingular

I don't know the address for other wireless providers.