That is a decal that I have never seen before. Your serial number definitely makes the motor a 1946 model, and the two piece cast tank makes it an earlier TD model.
The usual decal has all block lettering as in the style of the word ‘Johnson’ on your decal. The words ‘Sea Horse’ would be in the same style. Your decal looks similar, but not exactly like a 1949 TD-20, with the cursive lower writing.
Here is a restored 1947 TD-20 minus the lower cowl.
Improvise-Adapt-Overcome