“I’m respected in Turkey and I’m legal in Siam.”
Siam became Thailand around 1949 or so, and they currently have very strict laws surrounding drugs.
Not sure what the status was back when Brown wrote the song, but it’s not historically correct.
I think he must have heard about the older times in Siam, when the British basically forced them to keep opium legal so the British could profit from it. Maybe he didn’t know those days were over, or was just taking some artistic liberty.
Or he just needed a word to rhyme (kind of) with “Japan” :)