I can say yes for signatures but not for avatars. Since avatars don't have links, I wonder how the services they're meant to promote get visibility. I'm referring to avatar only campaigns, not those that combine avatar with signature campaigns because investors can simply click on signatures and get the information or web addresses they want.
Avatars carry the companies name, signatures do so too but with a direct link to the website, making things easy for whoever wants to access it. The only difference between them is that with the avatar whoever is searching has to do a little extra work to get the website (though some avatars even have the direct website on it, but you can't click it), and you just to type it in your browser, avatars are a good way to advertise, and people who are not lazy can easily find the website.
Although there are some projects at the bounty sections that allows you to apply their codes on your profile and then you being compensated with the little amount they wishes to dish out to your ranks level.
Do not advise OP to join bounty projects, he might never become a useful user in the forum if they do so, and his post history might end up being filled with only bounty reports.