Full Disk Encryption means your harddrive is encrypted.
With the command `sudo blkid` you should be able to see a crypto_luks volume (sda3 in most cases)
Other way is to use a disk utility program (that came with the distro) en check the partitions for a LUKS partition.
Go to system preferences -> security & privacy -> File Vault. That should be turned ON.
Hit the windows key -> type: bitlocker -> click on bitlocker manager