Well, I think only Signatures are useful as people can click on them directly as well as we get backlinks from it.
- Digital -
No doubt, Signature links are very helpful in getting more backlink for the website anchored through signatures.
- Link development
If you want to just spread the name of your site/business to the world you go with Advertisement option.
If you want to get backlinks for your site you go with link development option.
So, the avatar comes in "Advertisement" category and sig link comes in "Link development" category. Now you decide what you want to do
Hope I am clear with my points.