What highway was at this exit?

[TravelingBethelite]

Exit 170, I-35 South, Kansas...?

[NE2]

K-273 (which is even the street name on the Goog).
https://www.aaroads.com/forum/index.php?topic=5112

[Scott5114]

K-273 was decommissioned in 2002 because Williamsburg annexed out to the interstate, and Kansas policy does not allow routes to be in incorporated areas for their whole length.

[J N Winkler]

I suspect the exit tab may be part of the reason this sign was not field-modified to remove the excess green space, unlike the advance guide and exit direction signs for Garden Plain off US 54 following the removal of K-163.  (In Kansas, only Interstates have exit numbering.)  There are some signs on US 54/Kellogg Avenue in Wichita that did not have green space removed after K-2 and K-42 were pruned back, I suspect because they were all cantilever-mounted.

[ColossalBlocks]

I noticed something similar outside of Bonne Terre, Missouri.

https://goo.gl/maps/sSQqCzNmGxL2

There was a sign up i ahead that was missing the MO 47 sign and only had the K sign, and you could still see the outline of it, but MoDot fixed it.