The Financial Industry Regulatory Authority (FINRA) issued an investor alert on Thursday indicating that it continues to hear from investors, particularly seniors, who report receiving high-pressure sales calls urging them to buy penny stocks and other speculative investments.

The alert spells out the red flags that can indicate that a sales pitch is actually a scam, including promises of guaranteed returns, aggressive sales tactics and the touting of micro-cap stocks.

“Con artists engage in ‘pump-and-dump’ scams, in which victims are tricked into buying shares through a legitimate broker to inflate a stock’s price,” the FINRA alert states. “One elderly couple was talked into buying almost US$900,000 worth of virtually worthless micro-cap stocks. Another senior investor purchased more than US$500,000 of a micro-cap stock while on the phone with the caller.”

“Aggressive pitches and repeated calling, coupled with promises of high returns, can signal a scam. If you receive a boiler room call, the best course of action is to calmly say no and hang up the phone,” says Gerri Walsh, senior vice president for FINRA’s Office of Investor Education, in a statement.

FINRA reports that it has received more than 5,000 calls and recovered more than US$2 million for investors since it launched its Securities Helpline for Seniors in April 2015.