Here's what the swap header looks like:

At offset 0, the structure:
struct swap_header_v1_1 {
        char         uuid[16];
        char         volume_name[16];
	char         bootbits[1024-32];    /* Space for disklabel */
	unsigned int version;
	unsigned int last_page;
	unsigned int nr_badpages;
	unsigned int padding[125];
	unsigned int badpages[1];
};

At offset getpagesize()-10, the characters "SWAPSPACE2".

mkswap will have a -L label, and swapon will start accepting UUID= and
LABEL=, and that should about be it.