Ira easier to propose mutually sensible times if you know your opponents time zone.
Many of our players have flags, but not all.
Many of our players have finger notes on FICS which provide geographic info, but not all.
For recluses, spies, men hiding from their wives, etc, perhaps a United Nations flag, like Chess Tactics Server does...

Actually one problem is that nationality and geographical location isn't necessarily the same. For example you could have someone in Australia who came from europe and decides to keep flag of european country for sentimental reasons. It's far fetched but could happen :P

Having said that I have to admit that flags make things easier. Of course even timezones could have the odd exception if opponent works night shifts etc.

Solution I use is simply to make an early offer.

What could be useful to see is what starting time of opponent's previous matches were so you can see when they usually play their matches that should instantly get you in right ball park

Leaving aside the purely hypothetical cases of people who set their flag to a country of origin rather than a place of residence, I am not sure what the problem is here.

The point of game forum negotiations is for players to indicate when they can play, and come to a mutually agreeable time. The flags are just for fun.

One quite useful tool for finding out when players might be available is the FICS "log" command. This lets you know when people have actually been logging in recently. Rather more useful than a flag, I think.

Actually it's a good point about log command. It seems to be a pretty useful command and even covers last point I mentioned about time of previous matches.

Flags being for fun is probably best way to look at it :)

Granted that players put flags of their current place of residence. It still means nothing, because for example let us say most people work 9-5 in their time zone. There might still be players who want to play 1t 7 pm local time, 10 pm local time midnight local time and so on. Best is to offer, and past data of that player can be useful. I usually prefer around midnight in my local time

you also could use the database (https://www.ficsgames.org/) with the name of your opponent and the time setting of TL to find out about the preferred times by your opponent for 45 45 games by simply looking on when he played them.

The "log" command on FICS works even better for this.