IC: I = Indonesia, C = Cor-Tek (Cort), the serial number prefix is followed by a 2 number year. IS: I = Indonesia, S = Samick, the serial number prefix is followed by a 2 number year. For example "IC02" Made in 2002. In 2009-10 some Indonesian Squier's had the prefix ICS09XXXXX and ICS10XXXXX. There are a number of standard models that have the ICS prefix some are FSR but some are just normal run models. It therefore appears as though the the S in ICS is only an indication as to whether it is a Factory Special Run or FSR guitar (manufactured by Cor-Tek in Indonesia). It also appears likely that any FSR guitar beginning with ICS will be a Squier 'Standard' as opposed to any of the other models i.e. CV, Deluxe etc. Follow-up question: I understand it's supposed to be ICxx + 6 digits, but what does it mean if it's ICxx + 7 digits?
In your case though it is a Vintage Modified model. I'd say it is a Cort made one. I've also seen some serials starting "I" that were made in India. But ICS is usually Indonesia. The "10" means 2010 model year.
Hope that helps.
It looks like it could be IC + YYMMDD + xxx (or possibly IC + YYDDMM + xxx)?