Need to transmit 3 bits through window glass continuously
Serial encoding of the three signals would be appropriate. A cheap little microcontroller will easily drive a 38 kHz signal into a transistor switch, which in turn modulates an infra-red LED. Something like this.  A suitable protocol is SIRC (Sony infra-red remote). 
The infra-red decoder is already done for you in a simple, inexpensive three-pin chip used by TV receivers. Arduino and LINUX include software (LIRC) that can extract bits in the serial-encoded data stream on its "OUT" pin.
While this is not continuous transmission, it is very easy to implement. Hopefully, successive serial codes might be transmitted quickly enough to represent the state of your three LEDs.