UPDATE: John Watts, of Gypsy Knights Games, sent me this clarification regarding the Traveller System Reference Document, including info on use of the name "Traveller". Thank, John, for helping and not calling me a dummy!
Just a quick note: The Traveller SRD that you've found online is the portion of Mongoose 1e which was made OGL by Mongoose (with permission of Marc Miller). It can be used by anyone for any purpose so long as the proper reference is made in the required recitation of the Open Game License in the back of whatever publication in which this is used.
The Traveller SRD does NOT allow you to call your product Traveller, state that the product is compatible, or use the logo. That requires a direct license from Marc Miller or participating in Mongoose's TAS program.
This is why Cepheus Engine, Universal Machine, and Clement Sector products cannot have the name Traveller (or, indeed, use the word "Traveller" in them) on their product. While most everyone knows that these products are usable with existing Traveller products, it can never be legally stated that they are compatible.
But thanks for mentioning it! Much appreciated...and yeah...tons of backstabbery. LOL.