Having grown up in California, that's something I've definitely noticed about Oregon: reassurance markers are almost nonexistent on a lot of state highways
I have never found any consistency with ODOT for reassurance markers. Some areas are very well signed; there's even a stretch of U.S. 26 westbound in Beaverton that has three reassurance markers within one mile! But Oregon 99W, once you get off I-5 in Tigard...not a single reassurance marker until...ugh...I think on the south side of Sherwood. Oregon 99E has a number of reassurance markers in N.E. Portland (odd since that stretch is city maintained). Oregon 10 continues to be signed on Barbur for some oddball reason. But to this day the 15X secondary highways are unsigned (most of these are likely to remain in state jurisdiction for years to come) as are the 14X secondaries (some of these will probably revert to city/county control before too long).
Oregon 6 is another highway that seems to be well signed, with reassurance markers literally in the middle of nowhere.