This game has hidden development-related text.
What name could be more self-describing than Dokodemo Mahjong? It's a game of mahjong that you can play (almost) anywhere, after all.
Build Date/Dev Credit
Starting at 502D in the ROM is this small piece of text:
Copyright 1999 ADK Corporation Dokodemo Mahjong Ver 1.0 1999 March 20 by Makio Chiba MAHJONG ROM
Sound/Bank Test Texts
Immediately after that credit at 509A are some strings for the sound and bank tests.
BANK %x 0123456789ABCDEF 0000000000000000 SOUND CHECK PRESS A=ON B=OFF BGM NO.00 OFF EFFECT NO.00 OFF ON OFF OPTION MENU NOW SAVING PRESS B TO RETURN PRESS A TO EXIT PUSH D->SOUND CHECK