Safari replaces some text with an A
The symbol you see, letter A in a box with rounded corners, is most probably the generic glyph is used in some fallback fonts like LastResort. It means the data contains some Ascii (Basic Latin) character, and for some reason, a fallback font is used.

It’s more difficult to say. On the pages in the screen shot, the text rendered that way have Arial set as the primary way, so it almost looks like Arial was somehow replaced by LastResort in your computer. But this would affect the page more widely, and your use of the computer in general, so it’s probably something in Safari.

I would first try re-installing Safari.