Is it really needed in this forum? maybe yes or no, but for me it has been and still effective. This forum was made for people who is interested in Bitcoin and some Altcoins so I can say that this is one of the best place to promote your Crypto related things and ICOs. That's Advertisement is all about. Those posters with Signature in their account and making substantial post in different sections/topics in this forum attracts people to read their ideas(For me it's just like Newspaper).
Except there is a person who closes his or her eyes to interact on this forum then he may not see the signatures of other participants. For me, I see it as the best for of advertising in platforms like this. Maybe you haven't been clicking on adverts on others signature but I do it a lot. So I guess it is useful or should be useful for ICO promotion.