Yes, as long as the signal is 3V3 compatible.
You could use the Pi's UART RX pin (pin 10, GPIO 15) and the standard Linux serial software. That will handle standard baud rates (say up to 1 Mbps).
Alternatively you can use a general GPIO (any other GPIO on the extension header) and software serial. That should be good up to 19k2 bps or so.
On the first RPi :
In a first terminal : (create FIFO)
In a second terminal : (Write datas into FIFO)
readfifo-writeUART.py : pyserial short-intro
with serial.Serial() as ser:
ser.baudrate = 19200