Beware of Bitcoin stock scams; the Financial Industry Regulatory Authority warned investors on Thursday.

Red flags include pushy sales pitches -- such as those urging people to "Act Now!" -- or guarantees that an investment will perform a certain way. "Steep run-ups in price could signal potential manipulation or fraud," the industry-run self-regulatory group said in a statement.

It cautioned investors on Thursday about promised high returns from Bitcoin and other digital currency-related securities. The industry group specifically warned about "pump and dump" scams where promoters manipulate the shares higher by touting them to investors, then selling them before the correct value is revealed.

"It can be difficult for investors to avoid the lure of the cryptocurrency markets, especially when prominent people express interest in it and news reports and social media tout the promise of guaranteed quick fortunes and skyrocketing returns," Gerri Walsh, FINRA's Senior Vice President for Investor Education, said in the statement. "When legitimate companies enter a hot, new sector, con artists almost always follow suit."

While the introduction of Bitcoin futures on the Chicago-based exchanges CME Group Inc. (CME) and CBOE Global Markets Inc. (CBOE) has brought the cryptocurrency a degree of legitimacy financial regulators are stepping up vigilance and warnings as speculators and opportunists alike chase Bitcoin's 20-fold price surge this year.

Earlier this week the U.S. Securities and Exchange Commission suspended stock trading in The Crypto Co. CRCW, a sports bra-turned digital-currency company whose share price has surged 57-fold since September. The U.S. regulator alleged doubts about the accuracy and adequacy of the Malibu-based company's supporting disclosures to investors.

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