The symbol simply means that it's copy- and write-protected. In other words, the end user is not permitted to open the content for edit or make a clone of it in Content Manager. It should not have any effect on the Surveyor listings.
It's far more likely that the source of your problem is an asset that's not built-in or locked from editing. I remember someone referencing a list of products known to be faulty, among them the "Rusty Rebar - 40ft - Load" by arr. Check Trainz for assets flagged 'Faulty', then select all of those, right-click, and select "View Errors and Warnings" to clear any false positives.