The Liberty And Union flag, like the Liberty flag, consisted of the addition of the words, Liberty And Union, to the British Red Ensign.
As early as the Autumn of 1774, a flag employing the phrase: Liberty And Union was noted as flying at Taunton, Massachusetts. The Boston Evening Post reported on 24 October 1774 that: "We have just received the following intelligence from Taunton ~ that on Friday last a liberty pole 112 feet long was raised there on which a vane, and a Union flag flying with the words Liberty and Union thereon." For that reason, this flag is commonly known as the Taunton Flag.
It should be noted that various present-day artists who have interpreted the flags of the American Revolutionary War like to use sans-serif fonts for the lettering. Sans-serif fonts were not created and put into widespread use until the late 1800s. At the time of the American Revolutionary War the most popular font was Caslon. Most of the flags that were created at that time, which employed lettering, tended to have the letters painted onto the (usually) silk fabric. Such painted lettering would have been executed in the common font of the day ~ Caslon. It is possible, in some few examples, where the lettering was added to the fabric by separate pieces of cloth being sewn on, the letters might appear to have been sans-serif. Such examples would have been the exception to the rule.
Not to be confused with the Continental Union flag, the statement of the "Union flag" flown at Taunton would have been refering to the flag with the Union jack in the canton.
It should be noted that the flag flown at Taunton is basically the only one noted in contemporary accounts as bearing the whole phrase Liberty And Union.