In my experience, I've found that many work at home type forums are ok with signature links, but forums in other subject areas aren't. Sometimes, you will need to link to your own website, rather than use an affiliate link in your signature. If you don't have a website, you can always try linking to a Blogger blog or something like that.

Take it with a grain of salt man. There is a big internet out there, your gonna run into bumps along the way. It's all part of it.

Take care, Davin