Nothing says "welcome" less than bars over the windows – except, perhaps also adding a plywood barrier inside. With a small peephole, of course, for surveillance purposes.
Of course, in this window, there seems to be a small can for donations available – just in case you're so inclined!
This image is part of the excellent +#Window Wednesday series on G+.
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I like that little peek a boo cut out, just enough to see who passes by.