Coombes began his career at Chelsea in 2006. After almost eight years at Stamford Bridge he was released before joining Notts County.
He is remembered by County fans for scoring against Liverpool at Anfield in the Capital One Cup to send the match to extra-time.
Bromley manager Mark Goldberg said: “We needed to fill the gap out wide with the departure of Anthony Cook and the injuries to Louis Dennis and Pierre Joseph-Dubois so I’m delighted to welcome Adam, who has been training with us recently, and like Pierre and Louis has played both as a striker and a winger for his previous clubs Chelsea and Notts County.”
Coombes will be eligible for selection tomorrow for the visit of Tranmere Rovers.