Udev rules for usb device without serial number

# show device informations
udevadm info -a -p $(udevadm info -q path -n /dev/ttyUSB0)

# create /etc/udev/rules.d/50-devices-usb.rules to create a symlink 
# when an usb device is on usb port 2-10
KERNEL=="ttyUSB*", KERNELS=="2-10", SYMLINK+="ttyUSB.DEV1"

# reload rules
udevadm control --reload-rules && udevadm trigger

source: http://vncprado.github.io/udev-rules-for-devices-without-serial-number/