That would almost certainly not be upheld in court - Sega v. Accolade found that the use of a trademark as part of a security system cannot be prosecuted as trademark infringement.
Capsule summary: Sega's Trademark Security System, which was present in some versions of the Sega Genesis game system, would check for the string "SEGA" at a particular location in the ROM. When it found this string, it would display the text "PRODUCED BY OR UNDER LICENSE FROM SEGA ENTERPRISES LTD." on screen; if it did not find this string, the game would not boot. Accolade reproduced this to make their unlicensed games work; Sega sued them for a variety of things, including trademark infringement, and lost.
The gameboy would copy a section of the ROM onto the screen then checksum it. The gameboy would only jump to the real start address if the displayed bitmap matched the nintendo seal of quality. This went a bit further than Sega's system by displaying it verbatim. Every ROM needed to includ the full trademark and it would be show in full to the user.
I think they get this system for the Gameboy Color. I'm not sure of the timing between the lawsuits and the GBC. In general the GBC is a GB with double clocked CPU and palleted color so they might have kept the same scheme for developer ease.
http://en.wikipedia.org/wiki/Sega_v._Accolade
Capsule summary: Sega's Trademark Security System, which was present in some versions of the Sega Genesis game system, would check for the string "SEGA" at a particular location in the ROM. When it found this string, it would display the text "PRODUCED BY OR UNDER LICENSE FROM SEGA ENTERPRISES LTD." on screen; if it did not find this string, the game would not boot. Accolade reproduced this to make their unlicensed games work; Sega sued them for a variety of things, including trademark infringement, and lost.