This one read: "The same fence that keeps others out keeps you in."
This suggests that perhaps fences are not godly. Now it might mean that we shouldn't fence others out of our hearts - and a problem with short, pithy sayings is that they lack the nuance to settle things clearly. But how about "good fences make good neighbors"? The tragedy of the commons is the result when we lack fences. What we need are gates in our fences, gates that are open at appropriate times. But we need fences too.
Maybe I'm too critical: I look for something that would actually entice me or intrigue me enough to come inside. I can't recollect ever seeing a sign that did that. The ones that try to be funny are generally lame (true, brevity is the soul of wit, but...), & many that try to be serious (the "turn or burn" kind) are the sort of thinly-veiled vindictiveness that I have come to resent among Christians.
Having disagreed with the worth of church signage, I do agree with Andy on the subject of fences. Spiritual fences are essential to spiritual health, like psychological fences are essential for mental health. Having your soul run over roughshod is not godly. And we are talking fences, not barricades. If you've ever dealt with people who have serious boundary issues, either too loose or too strong, you know what I mean.
In terms of Orthodox spirituality, the virtue of "nepsis," or "watchfulness," is fundamental. We use the Jesus Prayer precisely as a guard to the mind, so that intrusive, passionate thoughts do not take a foothold &grow into sinful thoughts that lead to sinful actions.