G-dram

[cessna152towser]

It seems that the small craft I have seen in the US use a combo of numbers and letters, but I could be wrong

Correct - N followed by a combination of numbers and sometimes also one or two letters in USA.
G dash followed by four letters in Britain
C dash followed by four letters in Canada.
Here is a picture of my cousin preparing his Cessna 172 floatplane registered C-GEVE for flight on Shawnigan Lake, Vancouver Island, taken twenty years ago with Ann looking on from the jetty.