On 25th September 2010, the Bank of Thailand (BOT) had organised Thai Banknote Expo, a two day event to let public know more about history of Thai banknotes, identification of counterfeits, taking care of banknotes, etc. Extremely rare banknotes right from the 1st series to unissued varieties were on display following the theme "Best of Thai Banknotes".
One of the rarest banknote, a Series 1 50 Tical overprinted note, can be seen at Thailand: One of the rarest Thai Banknote.
Another very rare banknote, an overprinted 500 Baht from Series 5, is not even listed in any catalogs or internet sources. During the 2nd World War, Thailand was occupied by the Japanese invasion forces and all banknotes were printed in Japan. However, since these Japanese printed banknotes could not be delivered on time, many special issues were printed locally. Quality was poor and counterfeits were rampant. To take care of banknote shotages, uncirculated 1000 Baht banknotes were overprinted as 500 Baht. However, these notes were never ever issued and are extremely rare.