I have seen them all along the ridge infront of the radiator. The most common place is on the driver side. Here is a pic of my bone stock original 73 dart. It isn't the yellow one but my 73 scamp I sold had the yellow one in the same place (on the battery side).
Im pretty sure that anywhere along the core support is "correct". It's like the spare tire decal in the trunk that we just had a thread on, they just slapped it on where ever, how ever.
Before I stripped my 73 Dart down for primer, the yellow sticker was on the passenger side of the radiator support, about a half inch from the fender piece. There was a white anti-freeze decal on the drivers side of the radiator support about a half inch from the fender piece. THere was the Mopar replacement parts decal next to that.
I put it on over the VIN stamping. On a side note, I took my hood off today and took it to the body shop to have the underside painted. After the rest of my car looked so good, I had to paint the underside of the hood to match. I cringed though, because there was still a grease pencil marking visible. Looked like a "60".