also a very popular phrase nowdays in Greece isabout hiding money under the mattress..So you could say something like:
Stop hiding your money under the mattress. Bitshares / Nanocard / Bitcoin
Μη κρύβετε άλλο τα χρηματά σας κάτω απο το στρώμα. Bitshares / Nanocard / Bitcoin
or
Are you still hiding your money under the mattress? Bitshares / Nanocard / Bitcoin
Εσυ ακόμα κρύβεις τα χρήματά σου κάτω από το στρώμα? Bitshares / Nanocard / Bitcoin
However having said all that you need to know that people in Greece in general are not very familiar with bitcoin. Many people think about bitcoin that is some ponzi scheme of the internet.. You may be surprised but something like bitshares and bitassets that can always be traded in stable fiat values might sound much more interesting to a Greek now than Bitcoin..
Greeks will definitely prefer and will get more comfortable with biteur, bitusd, bitgold than bitcoin now..
So I am not sure if by mentioning bitcoin , you may drive people away..