Ulster-Scots are people or descendants of people who came to the province of Ulster from Scotland, mostly during the plantations of the 17th Century although it can include emigrations from before then and since.
Ulster-Scots don't exactly have a lack of flags, but a lot of them could be inappropriate for some people to use:
First thing wrong with these flags is the use the former Northern Ireland flag/coat of arms, and while a lot of Ulster-Scots live in N.Ireland many also live in Counties Donegal, Cavan and Monaghan in the Irish Republic, so these flags could be seen as inappropriate by them. Secondly they are evidently unionist, and while many Ulster-Scots are Unionist, one does not need to be Ulster-Scots to be Unionist, or Unionist to be Ulster-Scots.
The Ulster-Scots Agency I think used this flag for while but it was never a formal flag of the Ulster-Scots people:
This lack of a flag is highlighted on the Wikipedia page on the topic, where the Royal Standard of the kingdom of Ireland, Ulster Flag and St Andrew's Cross are used as associated flags but these are not definitive Ulster-Scots flags.
Some people have had goes at designing one I found these on Wikis, based on the Ulster Flag and Royal Banner of Scotland.
I really like the first one although I think it is just a little too complicated, the other I like the idea but would reframe from using the lion rampant as it is technically a royal banner and while it is often used as a second flag of Scotland, people have often been caught out and fined for using it.
My proposal for an Ulster-Scots flag is a combination of the Ulster flag, St Patrick's Cross and St Andrews Cross combined in a way similar to the Union Flag:
Nova Scotia flag, and Russian naval ensign, another example is Leonardo Piccioni's flag design for an independent Northern Isles.
While this flag is supposed to be universal and can be used by Ulster-Scots or people of Ulster-Scots descent all over the world, I think that the Ulster-Scots of the United States deserve a special flag of their own due to the impact of the Ulster-Scots (or Scots-Irish as they are known as in the USA) had on modern day America. So here is my Scots-Irish-American flag:
Same principle behind the inverted St Andrew's cross. With the American bald headed eagle supporting the red hand of ulster, the three stars can symbolise a variety of things such as Scotland, Ireland, America or past, present, future etc. The idea of using the eagle came from 1794 'Whiskey' Rebellion flag, which would have been used by Scots-Irish communities during that conflict.
Coat of Arms
I know most ethnic groups don't have, need or use a coat of arms, however fallowing some woeful attempts at heraldry by Ulster-Scots or people wishing to symbolise Ulster-Scots like this I think an exception is in order:
My design very much inspired by the Nova Scotia coat of arms is this:
The shield itself features an inverted St Andrew's Cross deface with the arms of the Province of Ulster.
The supporters come from both the former Scottish and Northern Ireland coats of arms. The Unicorn symbolising the ancient Kingdom of Scotland and the Elk the historic Kingdom of Ireland. They both carry the flag of their respective kingdom and bear the arms of it.
The base has stones from the Giant's Causeway (a symbol of civic Ulster pride) as well as the Shamrock (of Ireland) and the Thistle (of Scotland).
The crest based on the Scots-Irish-American flag has an eagle supporting six stars in a saltire again represent the significant contribution of the Ulster-Scots to the USA.
The motto is Scots for "Born Fighting" which is taken from the title of a book by US Senator James Webb, himself of Ulster descent who wrote a history of the Scots-Irish from Roman times to modern day America. It reflects the often turbulent history and recognises that often the main contribution of the Ulster-Scots in world wide British Colonies and the nations that came after them was a military one.