This is a very common problem. Everything - everything - must have a consistant character encoding. eg.
Files must be saved as UTF-8 (without BOM signature)
The database must use UTF-8 charset and preferably collate as well
The HTTP headers sent with the file from the server must be UTF-8
and the meta tag can specify UTF-8
Of these, the meta tag is the least important IMHO
If you are editing files, check your text editors’s settings
If these are saved and read from a WordPress database, check your wp-config file DEFINEs. *you may need to redo affected posts.