Why are characters turning into blocks? I have a Samsung Galaxy S4. On the lock screen and on pop up messages some of the characters are blocks. 
Here is a screen shot of it:



Screenshot - Block Characters (Click to enlarge)

I'm not sure if it's one of my apps that is doing this or if it's something else.
It looks like a glitch in the font rendering process. If it is an in memory glitch, you may be able to resolve it by restarting the device. If it persists across restarts, then it is possibly either a corrupted font file or there's a bug in the font loader. In either case, you'd want to try to see if a restart resolves it.