What would you do if you found a bike on the side of the road that had obviously had a sudden and catastrophic failure?

Example: Today I found a department store Schwinn mountain bike that had been 'overshifted' - chain came off the low gear in the back, bound between the spokes and the freewheel, and twisted the derailleur all to hell. Besides being unrideable, it's in great shape.

What I did:
I made a little sign out of a business card and a chop stick - it says:

Was that your bike?
(my) phone-number
You can get it back,
no worries!

Then I stuck that sign in the ground where the bike was and tossed the bike into the car. I will fix the derailleur issue at Freewheel Bike Shop with my vast quantity of shop credit, and if they call back within a month, they'll get their bike back (fixed) for nothin'!

Am I being too generous? Have I 'stolen' the bike? What would you do?