While a 'Sharpie' or other indelible ink pen can write on the plastic smart cards, friction and simple wear and tear can rub the ink off, over time. To prevent this, use a strip of tape to cover the markings, or use a label maker and print out the information, and attach it to the cards.
A CSLAN in a box on a shelf will drain the 'carrier' battery. The exterior battery usable life is 18 months, the 'carrier' battery is 6 months. A CSLAN that has been in a box on a shelf for 2 years has drained batteries.