7. Is there a ban on anonymous donations to political parties?

While anonymous donations are prohibited, there are no rules concerning other sources of campaign finance, including in-kind donations, loans, and media discounts.
Source: OSCE/ODIHR (2016), Republic of San Marino, Early Parliamentary Elections, 20 November 2016, OSCE/ODIHR Needs Assessment Mission Report, OSCE/ODIHR, Warsaw

Anonymous donations are prohibited (Article 13 LFPPM). That said, anonymous small contributions are allowed to be collected in transparent containers during conventions, festivals and events, and those amounts are reported under a relevant budget item.
Source: GRECO (2016), Third Evaluation Round, Evaluation Report on San Marino, Transparency of Party Funding, (Theme II), GRECO, Strasbourg