Strange numbers

Hello

I’m getting strange numbers, what look like error numbers (2d5f, 3b31, 2247, 2523 etc.) being displayed in two seperate installations of wordpress at different domains but on the same server. These numbers are appearing both front and backend of wordpress primarily on pages which show posts and pages (so backend not the dashboard, options etc.). I can’t see any link between the issues on both sites but to complicate matters even more I only get these errors at work behind a firewall, no such errors at home.

Anybody had this before? What is it?

a+
gar