My Thai girlfriend bought a piece of land and a home(on two different location but in the same Amphou)in Bangkok.I know I can't own land or house in my name,that's why I write "My Thai girlfriend....." .We know each other for 9 years and have a son 4 year's old.When we went to the government office to sign both contracts the officer asked a copy of my passport and give me a piece of paper to sign.I can't speak or read Thai fluently and asked him why I have to sign a paper.His answer was that Mr Thaksin want to know where the money came from.(not his words but a summery)If I not sign the paper my girlfriend could not buy.My question is:Do somebody know more about this?

You had to acknowledge that the monies paid were hers and you agreed to make no claim whatsoever against the property. That is a standard requirement.

Standard requirement for an unmarried Thai wife (with a farang (possible boyfriend?) lurking over her shoulder)? I know that is often asked for Thai wifes with farang husband, but for those who have not tied the knot???

Sunny

I didn't have to sign before my Thai gf and I were married - only since she became my wife and has my surname on her ID.

I understood that Thailand did not recognise de facto relationships?

Common law / de facto relationships are definitely not legally recognized in Thailand.