The American Locomotive Company is often shortened to ALCO, ALCo or Alco, no right or wrong way to shorten the name and we often use different variations.
The ALCO RS-3 was the builder's pinnacle in its early road switcher designs. While the American Locomotive Company would have some success in later Road Switcher (RS) series models, like the RS-11 and RSD-5, nothing would compare to the amazing success of the RS-3.
The ALCO RS-3 entered production in 1950 replacing its predecessor the RS-2.The RS-3 would go on to be the most commonly seen ALCO model across the country and remained in the company's catalog for more than six years. Today, numerous examples of this locomotive remain preserved, several of which are still operational.
Information from: https://www.american-rails.com/160017.html