Even though San Marino did not join World War I, some of its inhabitants joined the army of Italy as volunteers; in OTL, after the end of the war, the island of Arbe (now Rab, in Croatia) petitioned for annexation into the Kingdom of Italy but, in 1921, Italy ceded the island to Yugoslavia, and most of its Italophone citizens left.
What if Italy had given the island to San Marino instead, as compensation for the volunteers' help during the war? It is, after all, the birthplace of San Marino's legendary founder. ASB? Maybe, but it's a cool what if.