What does SIY stand for?

Aerosiyusa, SA - Mexico - FAA designator (FAAC)

Montague, CA - Location identifier - FAA (FAAL)

Shropshire Imperial Yeomanry - British military (DMA)

Sivandi - Language code (ETLW)

South of Ireland Yeomanry - British military (DMA)

Staffordshire Imperial Yeomanry - British military (DMA)

Sussex Imperial Yeomanry - British military (DMA)