My preston mitre templets [sic- catalogue spelling!]:

They are a little different from the ones shown in the 1909 Preston Catalogue reprint. They are marked
E Preston & Sons
EP (symbol)
Trade Mark
Here's a scan of the logo:
The catalogue lists three sizes: 3 1/4", 4 1/4" and 5 3/4". Looks like I'm missing the largest size.
Update: I was able to find the largest template with and without the half circle cutouts!

Here's a mitre templet similar to the one is the Preston catalogue:
The decal says "Smallwood Birmingham England". I found it at a tool meet for $5. Click here for details on casting a gage like this. Below is the Preston Improved square and mitre templet.