Signs in English used to be quite widespread in such gatherings. Same with pro-EU "protests" in Georgia, Armenia and back in 2014 in Ukraine.

English signs can mean two things:

• They want "the international community" () to notice them and do something.
• It is a lot easier to get the guys in Langley to approve your slogans when you don't try to make them read a foreign language.

I reckon that neither is going to convince any significant number of Russians of anything other than the fact that these libs are making fools of themselves.