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A common theme is
"Risk to on-road cycling from speeding traffic"
and the proposed remedy - upright signs or road markings.

Speed ruction is fine.

The (mis)placement of rectangular cycling signs near the building line
is often misunderstood as an invitation to cycle on the pavement.
The sign means: "Route recommended for pedal cycles on main road".
In urban setting, it should essentially be redundant, and not used.

The root cause is lack of proper provision for cycling.
The lack of available road width is used as an excuse.
Often there is enough width but it's (mis)used by parked cars.
So replace on-street parking with adequate cycle lanes.

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The "Op Close Pass" mats used by police show
cyclist 0.75 m from kerb
overtaking vehicle 1.50 m beyond that.

Assuming a cycle lane marking goes down the middle of the 1.50 m
that corresponds to a cycle lane width of 0.75 + 0.75 = 1.50 m
with the motor vehicle passing 0.75 m from the lane marking.

A cyclist in the middle of the cycle lane is naturally well-placed.
The driver instinctively tries to keep the vehicle about the same
distance from the lane marking as the cycle (but on the other side).
This results in the desired (minimum) passing distance of 1.5 m.

[I have no evidence for the following other than observation.]
Cycle lanes below 1.5 m width encourage cycling closer to the kerb.
They also allow drivers to approach closer, and less than 1.5 m.
In effect, narrow cycle lanes encourage close passes.

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