I agree 100% that it's about signaling, and that's why I find it kind of distasteful. It's a cheap and ultimately meaningless substitute for real activism, and it requires zero sacrifice on the part of these signatories. Even donating to the ACLU would mean giving up some small amount of money.

(P.S. Google and Facebook employees who've signed, can I expect you'll be resigning from your positions immediately? Your companies already have big, government-exploitable databases designed for [ad] targeting citizens based on race, religion, etc.)