VBA macro sheet digital signatures

I'm working on a VBA macro sheet and i'd like to have a few work colleagues digitally sign the sheet as the final step. I've done this with regular spreadsheets where no macros exist (.xlsx) however, when I added a macro (.xlsm) the sheet does not allow more than ONE user to digitally sign the worksheet. I'm using excel 2010, does this version accommodate for multiple users electronic signatures for macro books?