Can I transmit in the ISM band without a ham radio license?
Yes, that is totally legal Worldwide, no license needed.
Do you own/use a:


WiFi access point
WiFi on a phone or laptop
Microwave oven
Bluetooth on a phone or laptop


These all operate in the 2.4 - 2.5 GHz ISM band which is legal as long as the device
transmits less than (I think, correct me if I'm wrong please) 20 dBm = 10 mW

So in your case: no worries, perfectly legal ! Enjoy :-)