Small square with "A" inside - what is this?

[carmel barber]

Lately, I get messages that look like a small square with an A inside. Gobbledeegook. I tried to copy and paste a bit on this page but pasting it made it turn into ordinary text.
How can I fix it. Make and instructions step by step. I'm not a tech head.
Thanks guys
Carmel

 

[Cory Cooper]

Hello and welcome.

-Which version of OS X?
-Where is the text copied from and where are you pasting it?

Normally, that icon means the font you are using is either not installed, corrupted, or has been changed.

C

 

[carmel barber]

Hello and welcome.

-Which version of OS X?
-Where is the text copied from and where are you pasting it?

Normally, that icon means the font you are using is either not installed, corrupted, or has been changed.

C

Hi. This just happens when I click on some sites or open some emails. I think it is something to do with the text they are using.