This banner is said to have been carried during the 1745 Rising. This is much later that the English Civil War period, but we can still learn a great many things from this banner when thinking about what may have been carried by the ensigns of the ECW.
Firstly, I am very surprised by the amount of detail on this flag. Typically banners and standards carried into battle are to signify a unit's identity and their allegiance. This was easily done at the time with large fields of color and simple, basic iconography. I do not know the dimensions of the Am Bratach Uaine, but this Macpherson flag is by far the most detailed and complex example of this period I have seen in my admittedly short experience. There is a lot going on in the design of this flag.
Secondly, I was unsure until now if the clan motto "Touch Not the Cat But a Glove" was actually used on banners carried into battle. I'm happy to have a primary source answer to that question and will plan on adding the motto to the Macpherson flags I will be working on in the near future.
And lastly, Another motto or slogan, this one in latin, makes its appearance along the bottom of the banner. PRO REGE, ET PATRIA (For king and country). Again, this is something that I can include in some of my own ECW flag design now that I have a good source.
This is a beautiful flag and I look forward to seeing it in person when I make a trip to the Clan Macpherson museum in Scotland next year.