The lights bear a counterfeit safety approval marking, officials said.
Sample strings of lights tested by Underwriter's Laboratories showed a possibility of live electrical parts becoming exposed and causing either a fire or shock hazard, according to the fire marshal's warning.
The suspect lights, sold in a string of 100 or 150 lights or as sets of three or more strings, can be identified by a splicing connector located at the point where the individual groups of lights hang down from the main wires, according to the warning.
The splicing connector looks similar to one of the light bulb sockets, with wires protruding from both ends.
They bear an unauthorized holographic mark of approval from Underwriter's Laboratories with the numbers "E127358," "E127901," "E48723," "E64444," "E97593," "E115759," "E65770" or "E127522."
The fire marshal's office received information that the lights were being sold in some stores in the state, said Chief Robert Shimer.
But the office hasn't been notified of any problems associated with the lights, Shimer said.
The lights can't be legally sold in Maryland because they were not approved by Underwriter's Laboratories or another recognized testing lab, he said.
Anyone who has them should stop using them and return them to where they bought them, Shimer said.
The product, never submitted to UL for testing, was brought in by a UL inspector who saw it had a UL marking but didn't recognize it as an approved product, said UL spokesman Tim Montgomery.
The suspicion was verified by a database check that showed the UL approval numbers belonged to other types of products, Montgomery said.
The Consumer Product Safety Commission is investigating the matter, said spokesman Mark Ross, who said he can't comment until the Bethesda, Md.-based agency issues a press release.
Although two of the "icicle" light sets they bought seem to fit the warning's description, the sets have UL numbers beginning with "J," Gillum said.
To be on the safe side, he said, he plans to call a consumer hotline set up by Underwriter's Laboratories for more information.
Consumers can call the UL hotline, at 1-888-854-6275, between 9 a.m. and 5:30 p.m. weekdays.