One issue that I think is confusing many is that the 4 note musical horn (actually 3 as the re is repeated) you are likely referring to is in the video at the 3:38 mark, not 2:38.
If that is the one, in cartoon production it has the name of “Musical horn” or “Car Horn - Musical ‘re-mi-do-re’” Type.
It is possible that the toontown people made fun of the Sparton trumpet musical horn off 20s-30s some seller sources claim that it was a horn added to the Packard Cadillac model T, but others point at the Spartan horn as being customizable and bought as a separate kit to add to your old jalopy and pretend it was a “Studebaker” sound. (Maybe the toon creators made fun of one of their producer’s customized horn)
