I just did a walk on Las Vegas Boulevard and I didn’t see any of the 500 series highway shields that used to be around. The only state highway I saw was 159 on Charleston. What gives?...are minor state highways not signed in Las Vegas anymore?
The state highways in the Las Vegas area have never been particularly well signed (at least, not as long as I can recall having grown up there).
A few 100 series primary routes (146, 159, 160) are well signed on the BGSs along freeways, begin/end points are signed, and there tends to be decent reassurance (at least at points crossing other state highways). Interestingly, SR 564 (Lake Mead Pkwy) in Henderson also falls into this category as the primary Henderson gateway to Lake Mead, but SR 147 (Lake Mead Blvd) in North Las Vegas isn't signed from I-15 and doesn't have as much reassurance, despite being the primary northern gateway to Lake Mead.
The 500/600 series urban routes are hit and miss, with a lot more miss than hit. None of these (except 564) are signed on freeway BGSs. They tend to have the beginning/end points signed, but very little reassurance signage exists (if existent, it only pops up after crossing another state highway).
Also of note is that there is virtually no advance "JCT" signage when approaching other state highways either. (Boulder Hwy/SR 582 & Lake Mead Pkwy/SR 564 in Henderson is the only junction I'm aware of where "JCT" signage and reassurance signs exist in all directions for both routes.)
It's worth noting that conditions are substantially similar in Reno-Sparks regarding the area's 600 series urban routes. Only one primary route (SR 445/Pyramid Way) receives decent recognition.
The only part of Las Vegas Blvd, signed as SR 604, that is owned by NDOT is the part from Owens Ave to I-15 at exit 58. The Strip portion is owned by Clark County.
As of 2017, NDOT still maintains about 600-700 feet of Las Vegas Blvd/SR 604 surrounding the Tropicana Avenue intersection on the Strip (this is not signed). This is likely due to NDOT still having ownership and maintenance of the four pedestrian bridges at this intersection. NDOT's enhancement project on these bridges (updating the look to match more modern bridges further north on the Strip, as well as upgrading the escalators, elevators and associated electrical equipment) will wrap up in early 2018, at which point they will turn the bridges over to Clark County. I anticipate NDOT will turn over maintenance/ownership of the road to Clark County concurrently or not long after.