Personalized. If one finds a Rav-Kav with the owner’s name and picture on the back, he may not use it; he must publicize it and try to search for the owner based on the name. Even if he checks and sees it is empty, he should return it, as a new card costs ten shekalim, and one must return anything worth a pruta (Issue 74, par. 8).
However, after a long time, it is reasonable to assume the owner got a new Rav-Kav, so there is no need to return it. With respect to the value that remained on the card, the company transfers it to the new card. With respect to the ten-shekel value of the card itself, the owner likely already spent that on a new card and thus completely relinquished his old card.
Anonymous. If one finds an anonymous Rav-Kav, the value of which cannot be transferred to another card, he may keep it and use it, in accordance with the halacha of finding money. Although some claim it is considered something with a siman since one can determine the exact amount of money on it [and quantity can be a siman], since many people do not know the exact value remaining on their Rav-Kav, the owner will give up on it right away, as he will figure the finder will think he does not know how much value is on the card and will give up on it right away. Since it is like money, we can give it the status of money, which a person constantly checks his pockets for and certainly gives up on finding.
