The insignia painted on the sponson is composed of the regimental insignia and a three or two-figure number of the vehicle number. The regimental insignia is the combination of the initial of the regimental commander's name and "Se" in hiragana. "Se" is for Sensha(tank). The regimental insignia was changed as follows.
1st Commander era (from 1937 to 1939)
2nd Commander era (from 1939 to 1940)
3rd Commander era (from 1940 to 1942)
4th Commander era (from 1942)
Type 89 Medium Tank during the 2nd commander Tomio Hara era
The tanks of 8th Tank Regiment at Rabaul taken over by the Allied after the war were painted only with numbers and had no regimental insignia. I asked about it to a veteran of 8th Tank Regiment. He said that it is because the regiment became the Army direct-control unit. So, the regimental insignia was not painted on the vehicles.