Currently naming series is set in general, applicable to all companies.
As a general practice, it should be different for different companies,
We recently changed a lot of naming series for DocTypes to make it make it more generic and changing it again to tackle multi company seems hassling.
Besides ERPNext grants the power of great customization and with a little tweak this feat can be achieved.
company.abbr in its fetch_from input.SINV-.abbr.-.#### and set this as default.Thats it. So every time you make a new Sales Invoice and select different company, the naming series will automatically adjust for it.

Thank you for your suggestion.
I feel its Great Solution and smart implementation.
Closing Issue.
hello Dear , currently i have more than 15 company and i need to segregate the serial for each one kindly update the steps more clearly
Most helpful comment
We recently changed a lot of naming series for DocTypes to make it make it more generic and changing it again to tackle multi company seems hassling.
Besides ERPNext grants the power of great customization and with a little tweak this feat can be achieved.
company.abbrin its fetch_from input.SINV-.abbr.-.####and set this as default.Thats it. So every time you make a new Sales Invoice and select different company, the naming series will automatically adjust for it.