I was taught to never show my palm to a choir in the “police-officer-stopping-traffic” sort of way, since that gesture has the psychological effect of telling the singers to clamp up and choke on the sound.

Some people use the Palm to mean “sing softer”, but I don’t, so that’s always the unique gesture I use with my singers to signal “cease and desist”, eg. at the end of an antiphon when we don’t have time to append another verse.

And then Fist when we have to jump ahead to do something else before we can stop, such as a Gloria Patri or the last verse of Crux Fidelis on Good Friday.

I point to my head on rare occasions when we absolutely have to repeat something again from the top, such as a hymn in an outdoor procession.

I’ve always found these are sufficient from children to volunteers to pros, provided I’ve had at least one rehearsal with those singing, to establish that in this choir we start and stop and take all our breaths together, and if you don’t like that, there’s another church up the street where they don’t care....

Whatever cues you adopt (and there are quite a lot to choose from that are used by quite a lot of choirmasters) make them small, meaning that they don't take up a lot of space, like grand gestures. Such cues and directions are largely personal and reflect the choirmaster's symbiotic relationship with his or her singers. Make your cues and espressive directing very precisely and in relatively small space areas, and train your singers to watch them meticulously. Don't distract them with grand exotic gestures that take up a lot of space. Most of those who do a lot of hand and arm waving actually convey very little information and only make spectacles of themselves - first of all, they really are not in control, and in most, but not all, cases really don't know very well what they are doing. Those who really know what they are doing and have trained their choristers well will control them absolutely with minimal but precise movements. One out of many talents of a really accomplished choirmaster is the ability to control forty attentive singers with the minimal movements of one finger on one hand. Strive for this before graduating to more complex gestures. The more disciplined you are the more disciplined and accomplished will your choir be.

Another thing - I've seen too many choirmasters try vainly to keep their chant moving by furiously directing or pounding out every syllable. The result? The chant, whether Gregorian or Anglican, gets slower and slower, wooden and lifeless. Direct chant only by making flowing gestures on accented syllables or words, and text rhythm. This will result in chant that glides, as it should, from one accent to the next, from one phrase to the next in a highly pleasing, linguistic, flow.

More simply to answer your question - develop your own personal set of precise cues which will convey the messages you want conveyed. There are very few if any that are universal.