What is this?

Me and my friend have been seeing these crosses everywhere In our worlds. The first one is from a world while I was playing alone I think the seond and third one is from me and friends world this has happend to us many many times but these are the photos i have captured by screenshotting it's just not one world all 3 of these are from different worlds and we did not make it, what is the reason for these strange occurances? - I'll report to you guys again if I get more screenshots from my friend