From osi info: http://www.theocc.com/components/docs/initiatives/symbology/symbology_initiative_v1_8.pdf

Corporate actions that result in non-standard deliverable components will be identified by adding a numeric value to the end of the pre-event symbol (MSFT becomes MSFT1). This naming convention highlights non standard deliverable option contracts to all interested parties. This convention also supports contracts that undergo multiple corporate actions. Once a corporate action symbol has been assigned, it will remain unchanged throughout the life of the contract. This holds for contracts that undergo any and all subsequent corporate actions.