Is there a visual reference/cheat sheet available for the different symbols and icons used in DTP? It’s been awhile since I’ve used it. I’m wondering just now about the rightward upward pointing arrow swoosh and the split box or window-like icons Untitled.tiff (4.22 KB).
If these symbols / icons show up by a file can I delete it without worrying about loosing the original? I’m trying to delete unnecessary tags and when I send them to the trash their tagged documents end up there too.
See Help > Documentation > Appendix > Iconology
In your image, the arrow indicates the item is indexed (the original document is not stored in a database but is located elsewhere in your filesystem). The side-by-side box means there is a duplicate of the document somewhere in this database. See Tools > Show Info for path information about the indexed document, and for database locations of the duplicates. Before deleting documents you might want to examine the location of each duplicate. Deleting an indexed duplicate from DEVONthink does not delete it from the filesystem in its actual location. Right clicking an indexed item will give you a command to Reveal in Finder.
In other words, there is no harm in deleting the tags when one or both of these icons are visible on the tagged file.
The files are inside tags that got there unintentionally when I indexed my Zotero database. I deleted the tags but found the files “inside” the tags in the trash.
deleted
Usually not – to be sure, If you are seeing these symbols for a copy of a document in a Tags group, then make sure you have a copy of the document somewhere else in the database otherwise you might lose it.
Here “copy” refers to a duplicate correct?
I gather that deleting a tagged “arrow” file is safe because it is indexed outside DTP
Deleting a file that only has a double box could potentially be lost if the other duplicate(s) are in the trash at the same time… is that what you mean?
Yes, sorry for the imprecision. 
Yes – and if you delete the database instance, the document will not get reindexed. It will still be in the filesystem, but DEVONthink will ignore it. If you delete an indexed document, DEVONthink will ask you when you empty the trash if you want to delete the instance outside the database or just the indexed instance from inside the database.
No, it’s not what I mean. I mean that if the only instances of a document are contained in one of the tag groups that are children of Tags, then deleting the tags will delete all instances of the document from the database. It needs to be mentioned because readers sometimes purge tags and inadvertently purge documents too.
Is there icon for “tag children” or a warning prompt that could be set when the last instance of a file is being deleted from the database?
I am trying to safely delete about 1500 erroneous tags and it would be nice to have some visual indication of which files are connected ONLY with tags. This time I am pretty sure most if not all are indexed files so I should be safe. However, I will double check if I have unindexed duplicates.
Thanks.