In Database Configuration on the WORKORDER object (as well as all the other objects like ASSET) there are relationships to the DOCLINKS table which control which records are surfaced. Every customer is different on which attachments are relevant to the technicians, and you can control this by modifying the relationship to add/remove objects as desired.
For the vast majority of customers, the relationship used is named DOCLINKS. If you remove the ownertable='LOCATIONS' piece, (IE: UNION ALL select doclinksid from doclinks where (ownertable='LOCATIONS' and ownerid in (select locationsid from locations where location=:location and siteid=:siteid)) ) you will prevent attachments from locations showing on the WO.
There is a MAXVAR (SYSTEMLEVELASSETDOCS) that you can configure in the Organizations application in the System Settings dialog (Create asset doclinks at system level) that would change the relationship to DOCLINKS_ASSETID. The difference here is when assets move across sites, the attachments would previously not be shown. The product was enhanced to use a different relationship that would show any attachments that had been attached to the asset in any site.