in june 2009, GM has filed for bankruptcy. trading has moved from NYSE to OTC pink sheets, and the symbol changed to GMGMQ and later to MTLQQ. in november 2010 a new GM symbol started trading on NYSE. i am looking for the regulations regarding stock symbol reuse in the US. is there a minimum time that the symbol has to be out of use before it can be reused?
I doubt it is regulated per se. Tickers are part of the listing contract between a new entity and the primary listing exchange. The exchange will seek to please the new client with a ticker they want, while also trying to please its existing members by assigning tickers in a logical, mnemonic way.
Since both the revitalized company and the markets expected a re-use of the GM ticker, that's what happened.