depending on the phone (and whether its software is up to date), you already have two options—ON ANDROID—for this ameer:

1.) open grindr
2.) go to settings
3.) go to Discreet App Icon
4.) select the icon (from the 5 offered choices) of your choosing
5.) profit

myself, i like the "To Do" icon — it looks innocuous enough, and no one who might have access to your phone should be inclined to randomly tap on it

(of course.. ..i would find it odd if your phone doesn't have basic security functions which can prevent a normal snooper from just getting in without a fight)

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your second option involves your directly editing the app icon / display name itself — which you do have the power to do, any time

on my phone, my procedure for editing the grindr icon is my finding any functioning copy of the icon and then depressing it for about a second — depressing the icon makes a menu with an "edit" option pop up

i activate "edit" and i can go from there

also, you can always stash this icon away in a folder, if you wanna try to make it a bit harder for some random homophobic snooper to try and catch ya
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actually ameer: since i'm here, i should also mention (in case you don't know), on android, you can also change the various sound effects of your app; and you can even disable the "in app" sounds — though, i feel i should point out, the chances of a 100% straight person knowing how grindR sounds like is pretty small

still, you can buffer your discretion even further, with that method
on android