Ton of "differ in signedness" warnings?

When I compile I get a TON of "differ in signedness" warnings.
Everything compiles but I am wondering about the warnings.

Looking up the error it looks like "just ignore them" is the answer but
should I?

Why is there something like this:

unsigned char *message;

or 
static unsigned char *cause = NULL;

I am guessing these are strings - so why the unsigned?