0%, in terms of RIMM shares and negative in terms of other, better performing shares.
In cash terms you really need a handle on the risk free rate and the stock's beta to end up with a meaningful risk adjusted return calc. Then you could annualise it - hmm 360 or 365 days? - up to you. I'd use the natural base for continual compounding if this is for a prospectus.
Great question for Elite Trader, keep them coming!