New laws concerning the use of red plates (dealer plates) have just been issued. Red plates can now only be fitted to a car for 3,000km or 1 Month (whichever comes first). Exceeding this, or any attempt to obscure the plate number and/or use of damaged plates that cannot be clearly read will attract a fine not exceding 2,000 Baht.
Use of counterfeit red plates will attract a fine not exceeding 10,000 and/or 6 months to 5 years prison.
Anyone that’s ever bought a new car in Thailand knows that it takes 6-8 weeks to get your normal (white) plates. however according to the land transport department this delay is due to your dealer and/or finance company, not them. They say they can issue plates within 1 day.
Link to more info (Thai language):