here is a link to a Canadian site that shows markings for different tank units and periods
Untitled Document
this website shows the restoration of the non-firefly M4A4 Sherman taken off Salisbury plain training area just by me. To its original glory also shows the multi-bank engine which I think is an incredible piece of engineering in itself.
Restoration M4A4 restoration
the next link is to a website that shows all the Sherman types and differences between manufacturers
Sherman minutia homepage
there is another site but I can't find it on this computer that showed the unit markings so have to add it to another post.