This little Hexagram star thing is quite interesting... Perhaps resident Mongoose expert Waza can get to the bottom of this one.
If you check out Waza's website www.vintagemongoose.com it actually appears again...
Under the page which explains serial numbers, you will see a picture of the underside of a bottom bracket from a Team frame with the serial # CI7 48484 "T". Look closely at the top of the picture, and there it is again, the Hexagram star!
The one mentioned here from Ebay is a July 77 and the one on Waza's site is a September 77. There were 5441 frames made between them. I doubt it would have been a special factory run for one person. Or maybe it was... One regular and one Team both with that star? Maybe there was a few made for one particular important person. A sponsored rider maybe? Wouldn't their frames have only been "Team" then?
For sure we now know one thing, it wasn't a "one-off" personal stamp from one owner's bike. It certainly appears to be an "In-House" Factory stamp.
Maybe the original owner had stamped them both himself, but unless one of his frames ended up with the guy selling on Ebay and his other one somehow ended up in Waza's possession down in Australia 31 years later... Well, I doubt it.
Another Mongoose mystery to be figured out...

Waza?