has anyone seen this on the iMac

You have an incompatible third-party font manager that is in conflict with Apple's Fontbook utility.

Links in this old thread should help you resolve the problem:

Re: All I see is the letter "a"

Can you please tell us what iMac model you have and what OS version it is running? You found the forum for Apple hardware made before 1998, thus before the iMac existed. Very few helpers travel through here. With your computer information we can ask the Hosts to move you to a more relevant and active forum for your computer.

Hi Stephen ,

The problem is dressed by Allan Jones as he has tagged a link , please click on it and check it how to fix it 🙂