This is a stripped-down, simplified fork of signs_lib, which was then re-expanded to feature various street and highway signs.
There are three sizes of highway signs (2x1, 2x2, and 3x2 meters), in four color schemes, and your standard 2-up street intersection sign (left, and also available without the pole). The very small signs at the far right are standard signs_lib signs, and just shown here for scale.
Check your crafting guide to see the recipes, but in brief:
The intersection sign can be made from either a default metal sign, two steel ingots, and two green and one white dyes, or from a single green signs_lib sign and two steel ingots. The top-only part has the same recipe, minus one steel ingot. You can make the full-height one from a top part and a steel ingot, also.
Craft the 2x1 size highway sign from four dyes of the desired sign's main color, two dyes matching its edge color, and two default metal signs, then make the 2x2 and 3x2 sizes from two and three of those 2x1 signs, respectively.
You can also make them from two, four, or six green, blue, orange, or yellow signs_lib metal signs.
In addition to those is a whole bunch of signs of various sorts - stop, keep right, pedestrian crossing, various yellow and orange warning diamonds, and so on. Keeping to stuff that's useful in a Minetest world. Some stuff lets you add text (such as the generic warning signs, speed limit, US Route, and more), while other stuff is just static image signs (like stop, yield, do-not-enter, and so on).
All of the smaller signs are reasonably MUTCD 2009 v2 compliant, as much so as is practical in a voxel world.
Since this is forked from signs_lib, some signs use the same 15 px font as a regular sign therein, but at a different scale. Others use the 31 pixel font that was once included with signs_lib (for its high-rez option).
Here's the full library of signs as of 2018-10-03 (note that things like speed limit signs are editable -- if a sign looks hard-coded, it's probably just a generic image):
Download: https://gitlab.com/VanessaE/street_sign ... master.zip
...or browse the code: https://gitlab.com/VanessaE/street_signs
Depends: a recent MInetest build and minetest_game, signs_lib (commit 4ff54c9a or later)
License: LGPL 3.0 for code, CC-by-SA 4.0 for media and everything else.