I think the only way to automatically not show your signature is to not have one. You can change the settings so that nobodys sig shows up, and you can choose not to include your sig for individual posts, but I don't think there is a way to set a default where your signature and only your signature doesn't get show in posts.
There is a maximum size of 200 pixels for signatures that includes both text and images combined. Anything beyond that gets cutoff. You need to either move the text above the picture to get it to show (which cuts the bottom of the pic off) or resize the image so that everything fits.
Note, if I've gotten any facts wrong in the above, just ignore any points I made with them
don't believe a thing you read about the next gen Camaro -- as history has proven time and time again:
WE DO NOT TALK ABOUT FUTURE PRODUCT PLANS PERIOD FbodFather
Camaro5 Fest sub-forum