I've seen people kiss an aron kodesh (cabinet holding Torah scrolls) when they approach it and, if they were standing near it, before they leave it. Does this have any written source; or, are there known instances of authoritative individuals' having done (or advised) thus?
In Shivat Tzion it says to kiss the WALLS of the Shul because of their holiness, and I say Kal WaHomer the Aron.
There are sources for kissing a mezuza, such as:
[לפיכך, כשיצא אדם מפתח ביתו, ינשק המזוזה: [חיי אדם, חלק א' כלל ט"ו
And possibly the custom of kissing a sefer Torah stems from this.