This type of ink should not be that difficult to remove.
Sorry to state the obvious, but have you tried a diluted detergent such as diluted washing-up liquid on a cloth with vigorous rubbing?
Undoubtedly, the best option you have is to go to your nearest shop selling electronic components and buy an aerosol can of "foam cleanser". The stuff is made by Servisol amongst others but there are a number of own-brand products available including two in Maplin Electronics (www.maplin.co.uk)
Foam cleanser is a mixture of solvents and detergents which is very effective for removing all types of grease and grime from surfaces. All the same, they are not harsh products and are unlikely to affect the rubber face surface. Once you buy a can, you'll never be without one in the house!
You need to avoid like the plague solvents such as acetone or other organic chemicals as many of them will dissolve the rubber before your eyes.
I'm confident foam cleanser will do the trick for you.