The local ID should be included on your W-2 (assuming you have W-2 income).  Look at the W-2 to be attached to the local return--the ID should be there (i.e., I'd assume San Diego would be SD).

Hey, also, if you didn't have anything reported in the local amount box, both the amount and the ID will be blank on the worksheet.  🙂

It took me a while to figure this out.  You need two codes for different questions in TurboTax to figure local taxes: 

1. A code for your local ID (city, township, etc.), which you can look up at this URL:

https://www.adp.com/resources/tools/local-tax-code-locator.aspx

2. A code for your taxing school district, which you find through your state income tax authority.  In Ohio, that information can be found at the URL below, but I assume other states have something similar:

https://tax.ohio.gov/help-center/the-finder/the-finder