Darx
If you go here, and follow the link, it will explain the laws regarding registration, plates, insurance, etc.
Link removed
You may be able to get away with breaking these laws - sometimes.
1. All bikes in and around Bangkok have to be plated, or they will get in trouble. There are many rental bikes in Chiang Mai without plates, and you can usually get away with riding them. But occasionally you will get stopped.
2. You should have a copy of the registration book with the bike. This is rarely asked for, but needed for crossing borders.
3. All bikes must be insured. You can insure a bike without a plate. If your rental does not have a current insurance sticker, you may get in trouble with the police and you WILL be in trouble if you have an accident.
4. All registered bikes must pay road tax every year, and display the current sticker.
5. You must have a plate to cross borders. If it a rental, you will need copies of the owners ID card, and written permission to take the bike out of the country.
6. SOMETIMES, you can cross into Laos with an unregistered bike at Chiang Khong / Huay Xai. You will need additional documentation showing the legal import of the MC parts that turned into the bike you are riding.
7. Legally, you need an international drivers license. Again - rarely asked for, but required.
Also read the GT sites:
https://www.gt-rider.com/bikes.html
https://www.gt-rider.com/crossingborders.html
BobS
"The true secret of giving advice is, after you have honestly given it, to be perfectly indifferent whether it is taken or not and never persist in trying to set people right."