Motor Vehicle Registration
You must register your bike.
You must attach the license plate on your bike.
You must carry a photocopy of the registration book.
The Motor Vehicle Act of Thailand (1979) requires that you register your motor vehicle at the Department of Land Transport, which is under the Ministry of Transport and Communications. Upon completion of registration, you will receive a registration book and a license plate. Driving an unregistered motor vehicle is subject to a fine not exceeding 10,000B.
Typically, the registration process takes at least a few months. For cars, usually, a temporary red license plate is issued, which imposes restrictions that one can only drive the car during the daytime (not at night) and one cannot cross over the provincial boundary without prior permission. For motorcycles, however, the temporary license plate is rarely issued, which means that one is forced to ride the motorcycle without a license plate for a long time. In such a case, the rider is required to carry the receipt for registration application.
The law also requires that you carry a photocopy of the registration book when driving a motor vehicle, and show it to a competent police officer upon request. Failure to do this may cause a fine not exceeding 1,000B. There are two spread pages in the registration book where it states the first registration date, license plate number, engine serial number, frame serial number, your passport number, your address, your birthday, etc., together with your signature at the bottom. Copy these pages. Reduced copy is accepted. (ref. Legal Documents)
If you carry the original registration book, you don't need a photocopy. But having both the bike and the registration book stolen at the same time assists the thief to transfer the bike ownership easily, so you want to keep the registration book safe at home.
The registration book proves the ownership of the bike. Other than at police checkpoints, there are certain situations where the display of the photocopy of the registration book is required. Like, for example, when you lose a parking receipt at a parking lot, you will most likely be asked to produce a photocpy of the registration book, together with your ID card.
Documents required for registration
In case you want to buy a motorcycle which has already been registered in Thailand (transfer of ownership), or buy an unregistered motorcycle at a motorcycle shop (fresh registration), you need to prepare following two documents:
Passport / Visa
Until a few years ago, a foreigner was required to possess a work permit to register a motor vehicle in Thailand. This requisite was somewhat eased later to possession of a non-immigrant visa (of any kind). Moreover, since 2001, a foreigner with a tourist visa can register a motor vehicle in his own name. One thing you should bear in mind, however, is that Thai government officials are often unaware of recent changes in laws and regulations. So, if you're asked to present a work permit to register a motor vehicle, you must remind them that a tourist visa is good enough.
A foreigner must also produce some kind of official proof of his address in Thailand. Usually, this takes the form of an “address certificate” issued by your embassy in Thailand. Here's a catch. Embassies of some countries, like Japan, issue address certificates only to non-immigrant visa holders. The U.S. embassy, as I hear, issues address certificates, or “affidavit of residency” as they call it, to just about anyone with a US passport upon request.
An alternative is to get an address certificate from a local Immigration Office. In Bangkok, this requires possession of a non-immigrant visa, anyway, and the fee is 500B, which is cheaper than getting one at your embassy. The situation - and the fee - vary in other provinces. Immigration Offices in Pattaya and Phuket , for example, are known to issue address certificates to those with only a tourist visa.
Registering in someone else's name
This is a common practice among foreigners who have difficulty providing necessary documents. Legally, it is difficult to claim ownership against the registered owner in case of dispute, so you'd want to ask someone you think you can trust.
It is advisable that, if you intend to drive a motor vehicle in someone else's name for an extended period, you ask the registered owner to write up a letter of consent, allowing you to drive the vehicle. This is not a legal requirement and there's no fixed format, but it should be written both in English and Thai, should convey a touch of authenticity, and should be attached with a photocopy of the owner's ID card, countersigned by the owner himself.
This is one way to assure your ownership over a motor vehicle registered in someone else's name. You ask the registered owner to sign a blank “registration transfer form” (official form) and keep it in a safe place, together with the registration book. This way, you can register the vehicle in your own name when you have necessary papers, or you can sell the vehicle later, together with the registration book and the blank registration transfer form signed by the registered owner. To avoid future disputes, you also want to keep the sales contract and receipt of payment.