It will likely show up on the criminal history as dismissed pursuant to CA Penal Code 1203.4
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Most likely, the relief provided from expungement doesn't remove it from your criminal record, it allows you to claim you have never been convicted (in most forums) but doesn't "seal" it when applying for government issued licenses and other exceptions.
I'm not sure why you would go to the Police station to get a background check. If you are referring to a police report of the incident, it will exist there until they purge their records. If you want to know what exists in your official criminal record, or rap sheet, contact the DOJ online and request a livescan. They will send you a copy. They are the official custodian of that record and it is available to you.
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