In gay, leather & SM communities,
coloured hankies are used as a signaling code for finding partners to engage in sexual activities. (Yes, I am including SM in the umbrella of sexual.)
I flag grey left to signify I am a bondage top. There are a lot of other things I am into and tying people up isn't even the activity I do most often. However, it is a part of me that is central to my sexual identity. When my car was prowled 2 years ago and my rope bag was stolen, my initial reaction was that my sexuality had been stolen. "How will I ever come again?" Reason swiftly told me that was a bit more dramatic than the situation called for, and I was left with having to mourn all the firsts that I lost along with that bag. That experience taught me that this was a large part of my identity even though I bottom in my primary relationship.
Now, for Xmas last year, I did get a green hankie in my stocking, so I will occasionally put that hankie in my right pocket to signify I have a daddy. Occasionally,I will flag both grey and green. I think 2 hankies is plenty at one time, and may even be a bit too much advertising. Boiling your interests/identity down to one or two is not reductionism: it's focusing what you are advertising. Having more than 2 hankies in your drawer is fine; choosing the corresponding hankie to wear for the planned activities for a date or a play party is a great way to get into a specific head space. Wearing 3 or 4 hankies at one time may lead people to believe you are greedy or undecided. If you don't mind those perceptions arising in others, then, go for it.
I do know someone who has a hankie with 4 different coloured corners and he folds it so that all for corners stick out of his back pocket. I find that charming, if perhaps an overly specific partner/play request that may keep him from hooking up with fabulous people who may not be into all four of those things. I also think it looks much more tasteful than having the bulk and riotous colour that results from having multiple hankies hanging out your pocket.
When choosing which hankie you plan to flag with, decide whether you are flagging your identity or your preferences to attract partners. If I identify as a bondage top, but I am going to a play party looking to get tied up, I will be sure to have that grey hankie hanging out of my right pocket. Generally, I flag my identity rather than what I may be searching for in the realm of play or relationships. I fold the hankie so that two or so inches peek out of my back pocket. When I am on the prowl for play, I will fold the hankie fewer times so that a good portion hangs down out of my pocket in an effort to get more people to notice what my role in play is.
Be aware, the big, long
"hanky code" list that can be found online started as an April Fool's Day joke. Historically, the hankie code was a smaller number of coulours and what the colours meant varied from region to region. Take it with a grain of salt and have fun with it.