Showing New info added in Subdocument

I have a document to which users add comments as subdocuments. the subdocument holds comment text, comment added by, and comment added on fields in an array.

        comment: "some comment text",
        addedby: "bill",
        addedon: 2019-04-02 06:09:21.102"
        comment: "some other comment text",
        addedby: "julie",
        addedon: 2019-04-02 06:14:41.802"

I want to added some indicator (icon, color change, whatever) to show that new comments have been added, and then clear that indicator when the user clicks on the comments tab in the UI.

I tried setting a session variable of the count of the array, and a second of the original count, but this is just setting the icon on all documents displayed in the UI, and clearing it for all of them. I want this to only display on the row / list unit for the document on which a comment was added.

I’m using Blaze for templating, and feel like I’m close, but I wonder if there’s an easier / better / more elegant way to do this. Surely this has been done a lot at this point. Just not finding much about it.

As always, any help is greatly appreciated.

Also, this only needs to work while users are live on the system…not for when they leave and come back.