Tagging given tickets in the same queue with a text string?

We often have several tickets in a given queue that are stalled
pending a given event. After the event occurs, some of the tickets can
be resolved immediately, others will require more work.

Is there any way I can “tag” a group of tickets with the string “XYZ”,
meaning “ticket is stalled until external event XYZ occurs”. Then, in
my non-RT calendar, I can indicate “XYZ occurs today: un-stall all
tickets tagged ‘XYZ’” or something similar.

The tickets are different enough that merging them would be overkill
(they’re usually quite separate issues from different people that just
happen to be waiting on the same thing), and even setting the “refers
to/referred to by” field would be a bit much.

However, the tickets are similar enough that creating a separate queue
for them would be a bit much as well.

The exact date of event XYZ is not always known, so setting a Due Date
for the tickets would again not work well.

Of course, I could edit the Subject field to include “(XYZ)” or
something, but that seems dodgy, especially since end users/customers
will see that (I realize I can remove it before replying to the
ticket, but, again, that seems kludgey)

Is there a built-in way to tag/flag a given set of tickets without
using custom fields or anything complicated like that?

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new ideas and technology is unwise and ultimately futile.