I do use separate pictures in each desktop for ease of identification.
It would probably be helpful to use partitian names.
[note: uuid's scrambled for security]
--------------------------------------------
so here is a simple way to find the disk in use and it's unambiguous UUID
tod@tod-1204:~$ mount <<<<<< The Command
/dev/sdb1 on / type ext4 (rw,errors=remount-ro) <<<<<< The line I wanted to see!
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
udev on /dev type devtmpfs (rw,mode=0755)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)
none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
none on /run/shm type tmpfs (rw,nosuid,nodev)
gvfs-fuse-daemon on /home/tod/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=tod)
tod@tod-1204:~$ ls -l /dev/disk/by-uuid <<<<<< The next command
total 0
lrwxrwxrwx 1 root root 10 Sep 1 00:55 05cdfa19-c951-422b-be66-9871958f83ba -> ../../sdb9
lrwxrwxrwx 1 root root 10 Sep 1 00:55 0cc413fe-7bb2-4ff4-9fdb-b6b7767c55b1 -> ../../sdc1
lrwxrwxrwx 1 root root 10 Sep 1 00:55 26cbcb32-de2d-457c-9dce-de56a12e0c6d -> ../../sdb6
lrwxrwxrwx 1 root root 11 Sep 1 00:55 39bbcc4b-2f15-4e70-b09c-badc03e44e21 -> ../../sdb10
lrwxrwxrwx 1 root root 11 Sep 1 00:55 3cbaf86e-d6fd-4498-b446-1661aaf4364d -> ../../sdb13
lrwxrwxrwx 1 root root 10 Sep 1 00:55 486779e8-c99b-4900-b0b4-f735ee4d88e9 -> ../../sda1
lrwxrwxrwx 1 root root 10 Sep 1 00:55 6499a8e5-b6b4-5683-9135-4146728d7102 -> ../../sdb5
lrwxrwxrwx 1 root root 11 Sep 1 00:55 654bae5d-9440-4a44-a211-eb163336919c -> ../../sdb15
lrwxrwxrwx 1 root root 10 Sep 1 00:55 65eafd02-9a26-4355-817a-c29f97dd11cb -> ../../sdb2
lrwxrwxrwx 1 root root 10 Sep 1 00:55 89bad1f1-475d-4788-ae7e-b46c4a6b8479 -> ../../sdb1 << it's UUID!!!
lrwxrwxrwx 1 root root 11 Sep 1 00:55 a35899e2-bc3e-49dd-80f6-35f315cc426f -> ../../sdb11
lrwxrwxrwx 1 root root 11 Sep 1 00:55 a53bb68d-bd94-4955-9bf5-e38ef218c1fa -> ../../sdb14
lrwxrwxrwx 1 root root 10 Sep 1 00:55 ab568d75-3b9a-426a-b566-a61db8526a05 -> ../../sdb7
lrwxrwxrwx 1 root root 10 Sep 1 00:55 ae80baf7-6429-4932-91bf-c8ea269363ba -> ../../sdc2
lrwxrwxrwx 1 root root 10 Sep 1 00:55 CDF9-4CD0 -> ../../sdb8
lrwxrwxrwx 1 root root 11 Sep 1 00:55 BF99-21F0 -> ../../sdb12
lrwxrwxrwx 1 root root 10 Sep 1 00:55 BECCFE7C9CFE2F11 -> ../../sdd1
lrwxrwxrwx 1 root root 10 Sep 1 00:55 eef36365-3989-49c7-8e43-94bf03799a3c -> ../../sdb4
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But I think you are asking "where did I boot from?" which can be a very interesting thing to find.
I cannot think of any fingerprints left by the loader other than perhaps "boot-once" from grub.
Perhaps you can add a command in through a section of grub whereby you can talk to a file so you could query it.
See "README" in /etc/grub.d