Prevents Google from showing a Site Links search box.
https://support.google.com/webmasters/answer/79812
Widgets · Site Search
Get access to data on 385,860 websites that are Google No Site Links Search Customers. We know of 337,636 live websites using Google No Site Links Search and an additional 48,224 sites that used Google No Site Links Search historically and 171,862 websites in the United States.
Get a list of 385,860 websites using Google No Site Links Search which includes location information, hosting data, contact details, 337,636 currently live websites and an additional 264,067 domains that redirect to sites in this list. 48,224 sites that used this technology previously and 171,862 websites in the United States currently using Google No Site Links Search.