OK I am trying to mark boxes I looked for, are probably there, but I didn't find them.
Having read thru the messages, it seems tags are the answer, as in:

Tagging with a color is the best way to mark them without placing an X. Future searches can list ignore yellow or red tags. My reds are definitely will not search and yellow are unlikely but possible. I tag blue as definitely want to search and green that I would like to find but maybe a longer hike that would take more time.

Please point me to the way to use these-do you open the record page then somehow record these without entering either found or missing?
Is there some other way to access these?
Perhaps an entry in glossary under T would be helpful?

Thanks in advance...

You mark a box by viewing its listing, scrolling to "Your tags", selecting which tags you want then clicking "Save Changes".

Tags are super easy to use and very useful.

Just click on any box listing. Do you see the big grey rectangle that says "Your Tags"? There are two columns of tags, headed by yellow on the left and blue on the right. (Well, at least that's what I see because I'm a premium member and have 8 tags to choose from.) At any rate, just click on the check box next to any tag, select "Save Changes" in the grey box, and the letterbox will now be tagged with the tag you selected.

Also next to the "Your Tags" rectangle you'll see a question mark. Click it and you'll get a lot of info about using tags.

Suppose you tag several boxes yellow and you'd like to see a listing of them. Just go to Advanced Search, scroll down to the Tags and select Yellow, run the search and you'll get the listing of your yellow boxes.

I am trying to mark boxes I looked for....

The others have answered the question about how to mark tags well enough, but I'd like to point out that you can run an advanced search for boxes you've already found (or attempted to find). Those kind of tags aren't really necessary at all--AQ does it automatically for you! Finds and attempts will also show up in your online logbook without the use of tags.

It's also possible to mark multiple boxes with tags at the same time while looking at search results--near the bottom of the page at the end of the search results.

-- Ryan

I'd like to point out that you can run an advanced search for boxes you've already found (or attempted to find). Those kind of tags aren't really necessary at all--AQ does it automatically for you!

This of course is totally true if you've recorded the box as an Attempt. CorgiLover said this:

I am trying to mark boxes I looked for, are probably there, but I didn't find them.

which makes me think they were talking about boxes they looked for, didn't find, but didn't want to mark as an Attempt. Many of us tag boxes like that for ourselves. I tag them with a purple tag that I've named "Tried Box." Maybe I started looking for a box and ran out of time, or the clues weren't making sense that day, or whatever, but I'm flagging them for my own use as something I made a half-hearted effort to find.

By the way, CorgiLover, if you click on the pencil icon in the grey Tags rectangle, you'll find that you can edit the names of the different-colored tags, another very useful feature.

Finds and attempts will also show up in your online logbook without the use of tags

If you looked for it but couldn't find it, it's missing.
Whereas if I looked for it and couldn't find it , I just can't find it.

I was looking for some way to keep track of the boxes I need to keep looking for.

You are right about my intent- thank's for the info😊

and I mark a single box with multiple tags - "want to find it" gets one color; "clue printed" get another color, after I have taken that step; and "in my GPS" get a third color. That way I know whether I have done everything I need to do, or if the clue didn't make it through the printer, or onto the GPS. My 'want to find' list can change as I read through more of the clues, especially in a densely populated area. Sometimes it can take more than one session just to read through the clues and decide which ones to look for, which is the reason I wish the tags would show on the Map view of an area search. If I read every clue, but only mark some, then the next day it's hard to remember whether I read it and tagged it, or read it and didn't tag it.

You caught me at a bad time the first time you asked--I was hiking the Portugal Camino at the time of your post and couldn't really do anything about it at the time. But I saw your message then and bookmarked it to maybe do later as time permits. =)

And it's your lucky day! Time permits today!!!!

I didn't just add icons for the tags, though. I added all of the icons for boxes, trackers and events. (You know if I only include "some" icons, people are going to start requesting those that I didn't add. "But I want to know which boxes are drive-bys just by looking at the icons!" kind of thing.)

-- Ryan

This is awesome! Thank you, Ryan.

Marvelous! I have wished for this a long time ~ oooo let's go on a trip to try it out!

You caught me at a bad time the first time you asked--I was hiking the Portugal Camino at the time of your post...

Where is the "jealous" button?
:)