My eagle-eyed walking partner spotted it. Not sure I would ever have noticed if she hadn’t wondered aloud, “Why are there leaves on top of that sign?”

Three signs, actually — a yellow warning sign about kids (close proximity to the former St. Edmund School on Pleasant Street), “No Parking Here to Corner,” and “1 Hour Parking.” A clump of signs on a green pole with a green clump of leaves on top.

The first thing we noticed upon closer inspection is that the leaves are alive, not dried up and withered as you would expect if someone, for some reason, arranged a crown of leaves on top of a street sign for some whimsical lark.

In fact, this crown of leaves looked so healthy, we were forced to channel our inner Sherlock Holmes, who famously observed that if you eliminate the impossible, what’s left is the solution. This shock of leaves was flourishing and that could only happen with roots, and if these leaves had roots, they also had a trunk. After rejecting all the impossibles (e.g. the wasp’s nest nestled within the leaf cluster was not a disguised pot filled with soil because wasps were actively using it), there was only one place where that trunk could be — inside the sign pole.

A long, squared-off tube, featuring a series of holes on all four sides along its entire length, which meant we could peer within, led to discovering this was not just a sign pole. It was a conduit for a slender tree trunk, growing straight and “true,” which, in Old English, was the origin of the word “tree.” Stunted leaves and foiled branches were visible through the holes but none made it out of the holes, which would have been a dead giveaway that something alive was inside. It also meant that no nutrients were being diverted from the leafy mop on top of the signage.

Somehow, a seed must have gotten in through one of the holes, germinated in the moist dark soil, been irrigated by rain and snow, and even indirectly sunned, then rose until eventually it came out on top and found more direct sunlight. What are the odds?

Which makes this Irrepressible Plant No. 2. Last month I wrote about a shrub defying long odds — and passing, polluting cars — to thrive in front of the overpass divider at Harlem Avenue and North Boulevard. I found that plant’s persistence inspiring.

Alas, someone — most likely IDOT — found it annoying and in short order, it was cut down. The stump is all that’s left, which means that someone at IDOT must have actually read our newspaper and, even more improbably, this column, which is beyond my wildest imagining.

Let’s hope the village of Oak Park doesn’t take its lead from IDOT and execute this sapling, which has struggled so mightily to find its place at last in the sun. Better to remove the sign pole from around the tree, if such a delicate operation is possible. (Free the Tree! Watch the Wasps!)

Imagine if the village could do this with all their signs. That would take “going green” to a whole new level.

I don’t know if the hidden trunk will be content to remain within the restrictive confines of its present metallic cage. I’ve seen tree trunks that have incrementally oozed right through chain link fences. Imagine watching that in time-lapse video.

But if something is dispensable, let it be the signage. The yellow warning sign about kids is obsolete anyway, since first St. Edmund closed its school years back, and the subsequent Children’s School lease wasn’t renewed. Too bad. The students could have adopted the tree and cared for it as a science project.

As municipal mysteries go, this is obviously a micro-issue, yet it also touches on the macro: How does our man-made environment harmoniously co-exist with nature? How do we react when a tree grows up through a hollow sign pole — and succeeds?

It’s a good test of our values. How serious are we about “going green”?

What is the lesson here? Live and let live?

Or “nature finds a way” as one of my friends framed it. But what if we keep eliminating “way” after “way” until nature itself falters, then fails?

A better lesson might be “against all odds.” That’s where we stand right now: The odds stacked against us, which we actually stacked against ourselves (and continue to). We’re fighting to save the planet and the odds against are increasing.

Nature will do everything it can to find a way — if we don’t get in the way. However, nature can’t do it alone anymore. We can’t do it alone either. But every once in a blue moon, nature finds a way and reminds us: If a tree can grow up through a sign-pole and reach the sun, then what else is possible?

Let’s answer that question with the same irrepressibility as this tree has shown.

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