I have written the iso to an actual usb stick, and `# blkid` from my main OS gives:
 /dev/sdc1: PARTLABEL="Gap0" PARTUUID="f590b812-00b8-464e-98a4-267c918d71f6"
/dev/sdc2: SEC_TYPE="msdos" UUID="3AAF-A397" TYPE="vfat" PARTLABEL="EFI boot partition" PARTUUID="f590b812-00b8-464e-98a7-267c918d71f6"
/dev/sdc3: LABEL="GUIXSD_IMAGE" TYPE="hfsplus" PARTLABEL="HFSPLUS" PARTUUID="f590b812-00b8-464e-98a6-267c918d71f6"
/dev/sdc4: PARTLABEL="Gap1" PARTUUID="f590b812-00b8-464e-98a1-267c918d71f6"