How do I limit image size in Signatures?
SMF allows you to limit the images size in Signatures in order to keep your forum structure and to prevent overloading in your server.
Navigate to Admin > Configuration > Features and Options > Signatures.
In this page you will have some options to configure Signatures. Navigate to Maximum width of signature images (pixels) and Maximum height of signature images (pixels) and set the maximum width and height in pixels for signatures images.
Note that signatures must be enabled at the top of this page. They are enabled by default.