Can I search for all the documents using a certain custom icon?
Just a suggestion, Catherine, but if I were you I’d put your question in the Technical Support section appropriate for your platform - Windows or Mac - this sub-forum being more for sharing tips. You’ll probably get an answer more quickly, and even if you can’t do what you want to do, maybe there’s a work-around.
Although I agree with Hugh about the forum, I thought I’d throw in my ½p-worth here.
Icons are visual elements, designed to help you determine at a glance some attribute of a document by the icon they have, but that makes them less amenable for search operations, as they are presumably stored within the app or in another folder and referenced by a URL, not within the project itself.
What I would do, is give every document with a particular icon a label or keyword, which you can then search for, as metadata is project specific. It might also be possible, though I don’t know as my usage doesn’t require different icons and I normally only have 2 labels, to set it so that if you apply a specific label or keyword to a project, the icon may be applied automatically. As I say, I don’t know, but I can imagine there would be users who’d find that useful, but I will leave it to others to put it forward, if they think fit.