Good catch, I hadn't noted that label option was introduced into mainline busybox (patches had been around since a while).
tc@box:~$ mkswap -L Labeltest /mnt/hda6/tc2.swp
Setting up swapspace version 1, size = 268431360 bytes
UUID=c6a69d5e-520b-4944-be86-ffb5fa3d1f2a
tc@box:~$ file /mnt/hda6/tc2.swp
/mnt/hda6/tc2.swp: Linux/i386 swap file (new style) 1 (4K pages) size 65535 pages Label Labeltest
tc@box:~$ strings /mnt/hda6/tc2.swp |head -2
*Labeltest
SWAPSPACE2
... works like a charm, but I could still not see how exactly that would relate to the topic