In Ireland the red circle signs never mean prohibited, infact the exact opposite! If something's in a red circle it means that it's a regulatory sign and must be obeyed.. e.g. an arrow pointing left in a red circle = keep left. These are gradually being replaced by the standard European white on blue signs to prevent confusion!

Prohibited = Red circle with a line crossed through it.

No Entry (Unique to IRL as far as I know but very logical)
[Linked Image from europcar.ie]

Straight ahead only (one way system):
[Linked Image from europcar.ie]


Normal Yeild sign:
[Linked Image from europcar.ie]

Here's a Yeild sign in an Irish speaking area on the west coast:
[Linked Image from leafpile.com]

These also appear everywhere:
[Linked Image from accesscarrentals.com]

Our guy looks less like he's working with an umbrella:

[Linked Image from athlone.ie]

This one is VERY obvious: (At docks/rivers/quays)

[Linked Image from athlone.ie]