SQL query with Like operator with Leading Wildcards
What first comes to mind, is that if you are searching for some symbols inside the licenseplate that will always start, for example at 4th symbol (example data 123as43bvxxx ), and it will be always be fixed, you can consider adding computed persisted column to your table

alter table [table1]
add LicenseplateComputed as substring(licenseplate,4,50) persisted


And then create nonclustered index on your newly added computed column "LicenseplateComputed" 

After this you will be able to query your table

select top (30000) * from table1 where LicenseplateComputed like 'as43bv%'


and it will perform efficient Index Seek