Is this sign clear enough?

I would add "- It will make them sick" to the Do Not Feed bit, just to make it absolutely clear.

The problem with putting “will kick and bite” means that you have annoyed that people are at risk of harm and you know it. You have to be very very careful with wording. For example I don’t have WARNING Rottweiler is and will bite as that puts me at risk if she harms somebody, but I do have WARNING! Dogs on the loose and a photo of my Rotty.

Private - trespassers will be prosecuted.
Or NO PUBLIC Access

10ft fence?
Tbh, people are total morons, you are always going to get some. They don't think the signs apply to them.

So they are trespassing?

I've seen a sign which says 'Please don't feed the horses. Your kindness may kill them'.

Maybe just DANGER - KEEP OUT. Designed for morons who will read for 1 sec. No one can argue that is inviting them to feed your animals

I worked in a pop-up cafe with recyclable paper cups.

2 bins, one labelled NO CUPS PLEASE, other one labelled CUPS.

Over the weekend we made the signs bigger and bigger, underlined the word "NO", added exclamation marks all to no avail 😄

People are idiots don't read signs.

High electric fence attached to the mains with warning sign.

You could try
'Please stay well back, these animals are unpredictable and in ill health. You might injure them or they might injure you. You are welcome to take photos but please stand behind the fence.'

I think your issue is that this sign is very clear but if someone ignores this sign, there is literally no sign in the world they will heed no matter the wording because they are the main character and entitled to do as they please!

You could put “These are poisonous killer donkeys who will kill you in seconds” and these idiots will not read and will pet them.

So yes your sign is clear enough, but no it probably won’t help 🙄

Non horse people don't understand laminitis, they think carrots or veg are fine so we put I AM DIABETIC, PLEASE DO NOT GIVE ME ANYTHING. ALL MY FOOD IS TRACKED on our fields. Seems to have worked for the most part. We still get the odd idiot but the two biters see them off.

Brilliant Diagram! Extra points for use of colour. Gold star for letting the donkey speak.

STAY AWAY FROM THE WEE DONKEY
I would be tempted to put up something like ‘This summer, tourists like you have caused:

• 6 instances of food poisoning
• 4 vet call outs
• 23 bags of litter’

Can you get more brambles or something to make it less accessible from the road? Or make the other edge of the field more appealing to the ponies? I find it astounding that people feel there is a public right to pet animals - I certainly stop and look from afar but would never try to touch / feed / otherwise disturb them.

great idea re diabetic signs.

round our way though people feed them mouldy bread and allsorts. tipping grass clippings into the field is the most dangerous though.

Maybe something along the lines of
DO NOT FEED THE DONKEYS - DIABETIC AND UNDER VET CARE FOR DIETARY ILLNESS
and
DANGER ELECTRIC FENCE

people are stupid. and ignorant.

I think I had read somewhere that someone had put something along the lines of 'Warning - Equine Flu Risk - Please Keep Your Distance' which was quite effective for keeping the clueless away as they thought they were going to catch the next version of covid from the horses, rather than the actual meaning of the sign which was 'keep away from the horses as there is Equine Flu in the area and I don't want it getting passed on to mine'

Warning! Trespassers will be shot

Motion detection sprinklers and if you have a ring doorbell that can be placed within your WiFi......set it to motion sensor with siren......

A few years ago I was volunteering supporting some families. In all three families the mums struggled with literacy. I could text with them no problem, and they replied, they did not APPEAR to struggle, but when reading a letter from the school or doctor they panicked about what it meant.

I remember going into a building with a big sign on the door. It wasn't that they didn't read it. They just didn't see it, and didn't stop and look, and so didn't read that it meant something relevant to them.
For me as soon as I saw it, I saw the words and their meaning, because I can read quickly. So a sign saying
STOP - no dogs in building (or whatever) as soon as I have looked at it, I've read it. I came to realise that if you are not a good reader, you don't see the words on the sign and instantly decode them. To read it you must stop, focus and read. They don't do that, so they don't ever see what the sign says.
I (ex-teacher) was fascinated by this, and so I talked to them about it, and started noticing other people do it.
The STOP sign might as well have been a picture of a flower, because they did not look at it and see STOP, they looked at it and saw some writing that they didn't have the time to stop and decode.

I have nothing to add re the signs but this has made my week complete. I genuinely love this

Electric fence only way to manage idiots unfortunately

MIL used to have a sign on her horse field that said
I hate people, I will hurt you and then a photo of said horse