The signs must be properly posted per statute ... I am at home at the moment, but I seem to recall from recent research in my city that they must be posted to indicate the location "No parking between signs" or "... to the curb", or a sign must be posted every X feet ... and the distance is not too far - about 20 or 30 feet as I recall, NOT 100 feet.
15.20.070 Obedience to traffic signs.
Every operator and every pedestrian shall comply with and obey every instruction appearing on any traffic sign or other marking, which sign or marking has been erected or placed by authority of the board or commissioner or this Division 1. (Ord. 6544 Ch. 1 Art. 3 § 1319, 1954.)
15.20.080 Signs prerequisite to enforcement.
No provisions of this Division 1 for which signs are required may be enforced against any alleged violator thereof, if at the time and place of such alleged violation any sign required by this Division 1 is not in proper position and sufficiently legible to be seen by an ordinarily observant person. (Ord. 6544 Ch. 1 Art. 3 § 1304, 1954.)
15.20.090 Warning and directional signs.
The commissioner may place and maintain all official warning and directional signs necessary to proper control of traffic. (Ord. 6544 Ch. 1 Art. 3 § 13202, 1954.)
15.20.100 Regulatory signs.
The commissioner shall place all regulatory signs and other markings required or authorized either by this Division 1 or by finding of the board or finding of the commissioner. (Ord. 6544 Ch. 1 Art. 3 § 1303, 1954.)
You might very will prevail at a hearing if the sign is so far away ... I wish I had the DOT rules on signs present with me, but I don't. To start, you might consider checking with the county roads department and asking for a copy of their guidelines for posting of such signs.