High-visibility hand-held flags are available at some crossings, especially around schools. How should this be tagged?
The existing crossing:markings=*, crossing:signals=*, and (proposed) crossing:signed=* tags don’t quite capture this very well.
For reference:
Naturally, I must also mention the existence of Seattle’s crossing bricks 
My neighborhood has exactly this flag and flag holder at crosswalks near senior centers. They’re tagged as crossing:flags=yes, which occurs 28 times so far.
This looks like a job for hazard=dangerous_junction. And as an aside, if we’re talking about nonmeasures for dealing with this, I highly prefer the brick to the flag as they’re a lateral move for visibility but it at least tries to balance the playing field when your opponent’s fighting with heavy machinery.
Personally I’d consider handheld flags to be a crossing:flags=no situation as the flags aren’t a permanent fixture to the crossing. Replace the speed limit sign in this example with a crossing sign, where the flags are intended to be fixed long term to the sign, and then it’s be crossing:flags=yes in my mind.
I would probably tag that as traffic_sign:flags=yes on the traffic sign node, since they can appear on just about any kind of traffic sign. But maybe we could have something similar on the crossing itself, akin to flashing_lights=yes for slightly higher-tech flashing beacon treatments. I didn’t coin crossing:flags=yes for the handheld flags, but I see the logic, since it’s really about the provision of flags for the crossing rather than a sign fixture. One hopes that supervised=yes treats the crossing guard more humanely than one of those fixtures.
I was thinking more typically where the baton crossing flags you carry across tend to disappear rapidly as people don’t leave 'em in the holder on the other side or they all end up on one side. I’m suggesting portable flags aren’t worth mapping due to their inherently ephemeral nature. Fortunately, they tend to be a temporary stopgap in place of something more permanent like RRFB lights, a traffic signal, an island or some other actually effective and long term solution.
That’s probably true depending on the neighborhood. One of the flag holders in my neighborhood finally disappeared in favor of traffic signals a couple years ago, after at least a decade.
So far I’ve never seen the flag holders empty around my neighborhood, but I think that’s because the neighborhood association restocks them. Some nearby cities keep them stocked as an ongoing operating cost. Some other neighborhoods in my city have used actual flag designs. flag:name=* and flag:wikidata=* could highlight the use of non-safety flags, but this detail could get pretty ephemeral as you note.
Didn’t expect there to be much variation on the flag design given that the flag is defined in the MUTCD (as the ones that get mounted above signs that are being emphasized on a temporary but long term basis). I agree with you there that what flags are stocked would cleanly fall on the side of ephemera.
I’m a little surprised NBC News was that casual about a straight-up obvious hate crime. Though the realtor they interviewed really does seem to underline one of the reasons I left the west coast: Widespread rampant homophobia and an insistence that it’s someone else’s problem, not something that happens there.
Yes, as @Minh_Nguyen said, I think this varies by place. Here in Seattle, we have many crossings that have had flags for years. I’m not sure why we’ve kept the flags (perhaps budget reasons, low pedestrian traffic, to encourage pedestrians to make eye contact, because they might be more effective than RRFBs, or just to retain the more human interaction between driver and pedestrian), and while there aren’t always flags available (missing, all at the one), the “flagged crossing” nature of the intersection doesn’t seem super ephemeral.
Maybe a good analogy would be tagging an RRFB-equipped crossing even though the RRFBs might be nonfunctional sometimes (during a power outage). It’s still an RRFB-equipped crossing, just like a crossing set up for flags is still a flagged crossing.
It would be difficult to make verifiable, but should the criteria for something like crossing:flags=yes include the flags/flag holder being robust & likely to stay for a long time?
Thanks, everyone, for your responses!
I agree that crossing:flags=yes|no seems appropriate, so I’ll mark this thread as Solved. [Edit: or not - Solved function is not enabled for this forum category]
I can go ahead and make an OSM Wiki page for it when I have time.
Side note - I noticed that crossing:markings=*, crossing:signals=*, crossing:flags=* do not quite match the format of the proposed crossing:signed=* - @Minh_Nguyen, any thoughts on that?
*:signed=yes/no is a general scheme for just about anything, probably riffing off the venerable unsigned=* and unsigned_ref=* keys. A slightly different crossing:sign=* or crossing:signs=* key would likely cause more confusion than it’s worth.
On the bright side, if we later learn of a crosswalk that vends portable Stop/Slow paddle signs for visibility, you know what to do.
I created the Wiki page: Key:crossing:flags - OpenStreetMap Wiki
Of course, feel free to make improvements. I’ll advocate for the inclusion of this key in the PWG Schema 
