Step 1: Ask yourself: Is it a tree limb? If "yes", continue on your way. If "no", go to step 2.
Step 2: Look around. Is there someone who seems to have recently lost a limb? If "no", then leave the limb alone. Other than previously attached to a person, you don't know where that severed limb has been. Report the severed limb to the proper authorities; they will assure that the severed limb's owner is properly fined. (Most states have severed limb licensing requirements.) If "yes", ask the person if that particular severed limb belongs to them. (Important: Use common sense here; meaning, don't ask a guy standing there with one arm and blood spurting from his other shoulder if the severed leg in the street happens to be his.) Go to step 3.
Step 3: Offer to reattach the severed limb for no money down, no interest and no payments for the next twelve months. If the individual refuses this offer, back away quickly - he or she is obviously insane to turn down such a great deal. If the individual accepts - and make sure you get the terms of the agreement in writing at this point - go to step 4.
Step 4: Reattach the severed limb and give the individual a receipt for services rendered. Keep a copy for your records. Go to step 5.
Step 5: Spend some time thinking about what you have just done. Ask yourself: Could I have done this better in any way? How can I be more effective when I encounter severed limbs in the future? Only through patient and honest evaluation of your performance can you expect to improve. Go to step 6.
Step 6: You did a good thing by reattaching a stranger's severed limb and truthfully examining your performance. Provided both of your arms have not been severed, take a moment to pat yourself on the back.