I'm pretty sure Google has extensively tested the CTR's of SERP pages with and without the AMP logo. There's absolutely no way they would have implemented it if

I'm pretty sure Google has extensively tested the CTR's of SERP pages with and without the AMP logo. There's absolutely no way they would have implemented it if it resulted in a lower click-through rate. That would run counter to their own stated goals with AMP. Google tests and re-tests the crap out of things like this.