Hello I admit I don't know anything about the event in question. But I do very much like the badge and do believe it is of the period it advertises to be (certainly looks the part). A neat old pin that's perhaps seen better days but still nice indeed! Here's a link to a eBay paper advertising piece featuring the same image. Unfortunately I don't read Italian and can t be of more help. Very neat piece congrats! Best regards.
Raduno dei centauri - P.N.F. reale moto club d'Italia - Roma, 24 maggio 1933 | eBay
Hi; what you have there is a pin issued to celebrate a (national?) bikers meeting in Rome, 24 May 1933. The big "XI" stands for 11th year of fascist era (counting since october 1922) and "centauri" is a metaphorical way (centaurs) still in use, to define a biker.