The guy I bought mine from had it hanging indoors. He had 16" studs and made this bracket for it.
As you can see, there are 3 socket head cap screws threaded and welded to the 1/4" thick bar (68" long). The backsides of the screws went all the way through and then were ground off on the back side. The bottom of the heads are spaced 3/8" away from the bar. The cap screws are 31" O.C. apart from the head to the middle and 31.5" O.C. apart from the middle to the tail (This could vary from sign to sign). Then there were holes drilled every 16" to use lag bolts into the studs. This style may differ from your needs, but maybe something similar would work for you. I would prime and paint though to prevent rust.
You also mentioned, the side of your barn... If outdoors, don't forget about gusts of wind (and hang it high from thieves). Wind may be a factor indoors as well, if you have two large doors that open. I like Mikes safety chain idea.
Hope this helps any,
Steve B.