No such implication exists, but to avoid any misapprehension, the signs should read, in large, bold letters: “Obey the law.” Then it should give the appropriate citation to the law, and then quote the applicable portion. This way everybody is informed what the law is, not only at that location, but in all similar situations.
It raises an interesting issue. Suppose a town wanted to encourage people to get parking tickets as a source of revenue. So it passes a law saying that nobody can park their cars on Main Street (where there’s a big weekend flea market). Then they post prominent signs on Main Street saying “No Parking Mon-Fri”.
Out-of-towners drive to the flea market on the weekend, see the signs, and assume they can legally park their cars. Then the town police go up and down the street handing out tickets. When the out-of-towners complain, the town judge points out that there wasn’t any sign saying parking was allowed on weekends.
The simple legal principle is “whatever is not forbidden is permitted”.
The question is, how is a government supposed to inform people of the law? FOr obvious items, “ignorance of the law is no excuse”. IANAL, but I assume if a reasonable person should not have known it was against the law, then it is logical not to expect someone to know the law. Some laws have to be advertised, some laws have to be properly signed. (Many states and provinces have “Buckle up - It’s the Law” signs scattered all over the place, but try telling the judge you should be let off because you did not pass one…)
Parking is a good example. If a stretch of road is obviously not dangerous to part on, then unless there is a “No Parking” you should be able to park there, unless there is a generally known and easy to understand law saying otherwise. Even expressways often have “no stopping no parking” notices.
OTOH, many Canadian municipalities have a sign “speed limit 50Km/h unless otherwise signed” at most entrances to the city. Presumably, this is sufficient notice (and reasonable). Only exceptions need be signed.
“No parking Mon-Fri” and no other sign is misleading due to incompleteness and I assume would be tossed by the courts; presumably any sign would be complete - you are informing someone of the parking rules, and leaving out crucial information if weekend parking is not allowed. I have seen signs “No parking Mon-Fri 9AM-7PM, Sat-Sun anytime”. (Just as “no turn on red” presumably means you CAN turn on green…)
If the sign says “No parking Monday-Friday,” by implication that would allow parking on the weekends. The rule of “exclusion by omission” can be invoked in that case, although that is a stretch, but the rule is not necessary.