Eric,

You probably won't be able to 'identify' the stuff with any precision.

But, you can do some simple tests to see what it will 'work' for.

By far the most imporant thing to know is 'does it float?' and then 'how well will it float?'. Does it Absorb water? Is it colorfast in water? Will water desolve it?

You can find the answers to these with just a bowl of water and some time.

It's likely that it's poly yarn, since most macrame cord was. Once you've determined that it floats and won't either absorb water or disolve, you can use it for strike indicators. If it's colorfast (some of those dyes they used weren't all that great), then you can use it for wings, bodies, posts, etc.. That's if you care about fading/leeching of the color, if not, then it's useful for whatever.

Buddy