The biggest one for mine was just being quiet. I thought my mare was just getting old, but once medicated she reverted to her feisty self. She also got laminitis despite my best efforts. My other cushings pony just had a longer coat and looked scruffy. If you have a suspicion it’s worth testing because once you know, it makes management easier.
The first sign for mine was that he started stopping for a pee when being ridden. Never had done previously.
My friend's started getting rain rash which was also a new thing.
Mine was also being quiet, just not quite himself and maybe a bit spaced out. I couldn't out my finger on anything specific and didn't know what was wrong so asked my vet to take bloods and test for everything and this was what came back. Mine also went back to his usual self once he was medicated.
I agree that if you have a suspicion it's worth getting the test done just to find out and at least you can manage it accordingly then.
There are so many. My mare didn’t have any classic signs. She got very clingy - neighing and pacing at the gate, even out with her best friend. This happened again later when the prascend dose needed upping. Even though her coat didn’t look different I found it harder to clip (initially thought it was my clippers getting old and bought new clippers). So I asked my vet to test for cushings. He didn’t think she had it, said the test will come back with normal levels, but it didn’t (he’s a good vet that I trust, just saying this to emphasise that they can look normal..).
Mine had hoof abscesses that would heal normally and then reappear within weeks, and it went on for months. He came up within normal levels on the ACTH test but I asked for the TRH Stim test too and that showed elevated levels. He's been on half a tablet a day and hasn't had an abscess since (2 years).
I described mine to the vet as depressed, when vet saw her she said she didn’t think she had cushings and was very surprised with the reading of 172 she was on prascend for a short and went back to being perky and very lively to ride. Although I loved being able to ride out calmly I knew something was wrong..