I had a 2006 Triumph Rocket III Classic, and I BELIEVE it fit that, although I never fitted it. Having said that, all the other parts I bought at the same time were for that model.
On the bottom of the main seat it has the following - SDM Selvazzano (PD) Italy 4020224 and a sticker that says SDM 2301501. Triumph 2301820. (I think, as it's worn away). See pictures.
On the bottom of the pillion portion it has the following - SDM Selvazzano (PD) Italy 4020226 and a sticker that says SDM 2301821 26-04-4. Triumph 2301821.