Identifying TubeValve with a felt Marker is it safe ?

[baguadao]

I am using a Audio Research preamp Ls5mk2.
It has 10 tubes.
I see on the Owner's manual they are slotted into their respective positions in the preamp.

I want to mark each one of them with a ordinary marker so that if I remove them for whatever reason I can remember which tube/valve goes into which of the 10 positions.

My enquiry is can I safely use a felt marker like a YAMAMO Name Pen or a FASTER Name Pen to do it.

Thank you.

[Ali Tait]

Yes no problem.