Well I guess that could be done, specially if anyone wanted to gather an exact number for statistic purposes or something like that, but I guess we all know that the spam would disappear, and probably a lot of users (mostly farmed accounts) would disappear as well. We can't deny signature campaigns are a huge business in this forum. Projects that run sig campaigns here, pay a lot to the users that are wearing their sigs. The payouts have decreased overall, but considering the number of users in each campaign, and the number of campaigns running, I would say it's a very big number.
If I go to the overview campaign thread, and look for the average legendary member payout, which I would say it's 0.01 per week, we are talking about an average of $360 a month for a few posts (considering BTC at $9k). This is not an over extended figure, so I would say it's really quite easy for a legendary member to get at least $360 for a few posts.
That's a really nice extra income, and in some countries that's actually quite a lot. If someone uses alts, they can probably win more here than they would on a normal job (again depending on the country they live). Given this, I would say it's easy to assume, that if this option would disappear, people would stop spamming.I still don't think this is the best way to solve the problem though, because advertising plays an important role in the crypto ecosystem.
Forum sections where it's not allowed to use sig are a good way to create good sections free of spam, and the merit system is a good way to promote good content and to prevent account farming. This is why I think we are going in the right direction here.
Don't know if more measures will be taken or not, but I would say these two alone, will help a lot.