Ohio's grid-traceable spec dates to 1975, with a modification in 2004 which apparently consists entirely of changing the code identifying that type of sign. In 1975, "downloadable" and "vector" didn't quite have the meanings they do today, and likely wouldn't have been helpful to contractors until about a decade ago anyway.
That is just the problem. Back in 1975 you could still fake the Ohio route marker without using the actual grid drawing, but most of the methods available with 1970's technology were no easier, and often more difficult. For example, you could have used the Ohio piece from a child's puzzle map of the USA but that would still have meant tracing something, and if you were going to go to that trouble, you might as well use the official drawing. With the widespread availability of vector design packages and free clip art, we are now in a situation where unofficial Ohio outlines are considerably easier for contractors to access than the official ones.
I have just checked the current edition of SDM
on the Ohio DOT website and it looks like there still isn't an officially endorsed vector representation for any of the Ohio state route markers, unless you count the example shields in the M2 series designs (which, unlike the route marker designs proper, have largely been remastered in CAD). Indeed the route marker designs are raster scans of the 1975 versions.
BTW, although the current drawings date from 1975, the grid tracing concept is much older. Long ago Ohio DOT used to maintain traffic sign designs as a series of standard plan sheets which were included in signing plans sets as needed. I have, for example, a standard plan sheet dated 1963 showing--against a grid--a combined one, two, or three-digit Ohio guide sign state route marker (39" x 36" with 15" Series C digits). (I think there were cyclostyled traffic sign drawings in the 1930's, but in more modern times I suspect the SDM
was introduced partly so the signing standard plan sheets could be eliminated from plans sets, thereby reducing overall sheet count.)
I would fully support a move to OH route markers that use a simplified outline which can be fully described by a dozen or fewer segments (lines or arcs) whose endpoints and radii can be distributed on a standard drawing as well as a small SVG file. And the wide version should still be a separate spec.
I would suggest additionally that it should be made available in multiple vector formats and it should be a standard contract requirement that one of those specific files (not any others which the contractor may have on hand) be used to fabricate the shields. And then that contract requirement should be enforced, if necessary by rejecting otherwise acceptable signs with non-conforming Ohio outlines and requiring the contractor to eat the abortive cost.
And for illustrative purposes about state outline designs, I present:
I like those. Ideally, Georgia's should look almost identical.
Missouri is even worse than Ohio in that the state route marker design is contained in a Standard Highway Signs
supplement which is not on the MoDOT website and cannot be obtained by a member of the general public without difficulty. On the other hand, MoDOT has centralized guide sign design, unlike Ohio, and this may make off-spec outlines easier to police.