I have been writing my initials onto the dogbones (webbing connecting biners) of my quickdraws with a sharpie (permanent marker) so I can tell them apart from everyone else's. Recently, one of my climbing partners suggested that I should switch to marking the carabiners with tape or nail-polish instead, since (he claims) sharpie damages "soft" gear. What evidence is there to suggest sharpie or other markers can damage soft gear such as dogbones?
My quickdraws are Black Diamond FreeWires. The manual can be found online here. As far as I have seen, black diamond does not recommend against marking soft gear with markers. The closest statement I can find in the manual is
Care and Maintenance
Climbing gear must not come into contact with corrosive materials such as battery acid, battery fumes, solvents, chlorine bleach, antifreeze, isopropyl alcohol or gasoline.
After contact with saltwater or salt air, always rinse and dry textile products, and rinse, dry and lubricate metal products.
On the other hand, Petzl's manual suggests against marking slings in this infographic taken from the technical notice for one of their quickdraws.