Pain, not using limb, limb looks bent or swollen, whining, hiding, dragging or scooting across floor, unable to walk. Obvious fracture, bone protruding.
Immediate veterinary care is needed. Your pet will be in pain, so muzzle your pet before moving them. If there is excessive bleeding, apply pressure with a towel, t-shirt, or other available material while trying not to move the limb. Do not pull on the limb in an attempt to align the fracture. Stabilize the limb as best you can using a stiff item such as cardboard, rolled newspaper, a yardstick, etc. Do not give any pain medication unless instructed to do so by a veterinarian.