The "x" traffic sign typically means that the road or lane is closed or blocked ahead. It is used to indicate that drivers should not proceed in that direction.
An octagon traffic sign typically indicates a stop sign, meaning that drivers must come to a complete stop at the intersection before proceeding.
A red "X" traffic sign on the road indicates that the lane is closed and drivers should not use it.
That traffic sign is called a "crossbuck".
It means the road may be slippery, proceed with caution.
A sign with a straight line and a crooked line generally means that motorists need to merge.
The x road sign indicates a railroad crossing ahead. It serves as a warning to drivers to be cautious and prepared to stop for oncoming trains.
warningA merging traffic sign an example of a warning.warning signyellow diamond
An advance railroad sign is round and has a yellow background with a black X and black R's on each side of the X. The sign at the site of the tracks is an X shaped sign that is white with black text and says "Railroad Crossing" with the words crossed on each leg of the X. Crossbuck.See the related link for a site with pictures of US traffic signs.
A stop sign
traffic signal.
warningA merging traffic sign an example of a warning.warning signyellow diamond
policemen Also, stop signs and traffic circles (or "roundabouts") - altho they don't stop traffic, they perform the same function. From @MunicipalSigns: A pedestrian crossing sign (especially in California). A School Crossing zone. A railway crossing zone (Circular yellow sign with "RR" and "X")