Just for the record:
I got "existing signature left on the device" message when trying to add a LVM iSCSI storage. The problem appeared when I deleted one I had already created. Most probably I deleted it by the "novice" way and so I managed to mess something up.
I got it solved by following this link: https://blog.thewatertower.org/2019/01/02/cleaning-signatures-off-disks/
I got "existing signature left on the device" message when trying to add a LVM iSCSI storage. The problem appeared when I deleted one I had already created. Most probably I deleted it by the "novice" way and so I managed to mess something up.
I got it solved by following this link: https://blog.thewatertower.org/2019/01/02/cleaning-signatures-off-disks/