If you hold a class A certificate, you can, in addition to your main call sign, be granted a short call sign (only one) via the form.
Extra series of OO to OT call signs, in the format of OOxA, where x=0 to 9 and A= A to Z can be applied for.
Each additional call sign entails an application fee (€59,92) as well as a yearly fee (€59,92).