What does YOS stand for?

Oil Storage Barge - Non-self-propelled - Navy symbol

Years of Service - Army

Yoper Operating System

Yos - Language code (ETLW)

Yosemite, CA - Amtrak Busline code

Yosiwara - Japan - Seismograph station code, US Geological Survey - Closed (SEIS)

Your Obedient Servant - Closing of a letter or post - Civil War term

Yttrium Orthosilicate (SAUS)