In short: the Financial Supervision Commission (FSC) is Bulgaria's authority for regulating and supervising the non-bank financial sector — insurance, investment firms and funds, and pension insurance.
Simply put: Every EU country has a national financial supervisor that licenses firms, keeps public registers and receives complaints; across the EU, ESMA, EBA and EIOPA set common rules. In Bulgaria the FSC covers the non-bank sector, while banks and payments are supervised by the Bulgarian National Bank (BNB) and traders by the Consumer Protection Commission (CPC).
Example: Someone phones you offering an "investment" returning 3% a month. You search for the firm in the supervisor's registers and cannot find it. That is a signal to stop and report it.
Watch out: a licence means the firm is authorised and supervised — it does not guarantee a profit or replace your own checks.
Example: Bulgaria — the FSC also licenses and supervises pension insurance companies; insured persons can report breaches to it (Social Security Code, Art. 174(1)). Registers: https://www.fsc.bg/registri-i-spravki/
Check in your country — the name of your national financial supervisor (often a "financial supervisory authority" or "securities commission", sometimes the central bank) and its public register.
Source: FSC — https://www.fsc.bg; ESMA — https://www.esma.europa.eu