Yes the term "Tank destroyer" was applicable to M50 Ontos , but there was no official TD "patch" post WWII as "Tank Destroyer" was a separate branch within the WWII organization and operations of the AGF.
Now saying that, we know the GI was adept to using well known designs from WWII up to and including Vietnam. Some I can thing of is Ranger Diamond (subdued), 5th Ranger Bn subdued, the Korean war 187th Rakkasans subdued and color again these would of been individuals who had served in the units during previous conflicts and had them made for themselves and possibly others who served.
I would also hazard a guess the TD emblem would of been used in some other unofficial usage during the 50's and 60's but there would need to be more research.
Here's my TD with Hellcat tab