Its a yellow sticker next to the filler plug that says 'Use LSD oil only', the stickers seem quite durable and are usually still there.
ECU repairs, modifications and diagnostic interfaces for OBD1 Suzukis:
2006 Jimny, 1.3 VVT, stock
2000 Vitara 1.6 8V, Calmini 3+3, 33 MTs, 5:83R&Ps, remapped ECU
1986 SJ413K pick-up with G16B conversion