I'll look into this when I have time, after returning from the road. But as a frequent visitor to Deming, I've seen the US 70 and US 80 shields on I-10BL going back several years, and written them as remnant old signage. i also don't recall any signage on I-10 indicating that US 70 leaves the Interstate to pass through town. I've also seen the US 180 signs in Deming south of I-10, and did not take them seriously (that applies also to much of the other route signage in NM).