Anything with ring tip AND sleeve is a stereo signal lead.

Anything that weighs a ton is a speaker lead (heavy copper conductor).

Anything that you can look inside the jack plug, look, and if it has shielding it's a guitar lead.   

Anything else, plug one end into an amp and the other into a guitar. Have you shedloads of hum, and other leads not so much hum? The hummy ones are unshielded and are probably speaker leads.

Anything else you COULD try sticking a pin through. If it goes very very quiet it is PROBABLY a guitar lead and you have shorted the shielding (earth) to the core (signal) hence blissful silence.   But you MIGHT have managed to get both cores on a speaker lead.

OR with a sharp knife gently pare back the outer. If you find a metal shielding, it's signal. Repair with insulting tape and use for guitar. If you find different coloured insulated wires and no shielding, it's speaker. More insulting tape and use for speaker.

If all else fails find someone who can solder, and cut one end off which will reveal the internals and solder a new jack plug back on.