Some signs of rip currents include:

A difference in water color. The water may be murkier from increased sediments or appear darker because it is deeper.
The waves may appear to be larger and choppier.
Foam or objects are carried directly out to sea, or debris or vegetation may appear perpendicular to the shore at the site of a rip current.
As the water rushes out to sea, a bowl-like indentation may be apparent on the shore.
Rip currents are usually present if the surf is very rough. Remember, always use common sense and swim responsibly.

If you are caught in a rip current:

If you are caught in a rip current, don’t panic or try to swim against the current. Swim parallel to shore until you are out of the current. Rip currents are rarely more than 30-feet wide. If you can’t break out of the current, float calmly until it dissipates, usually just beyond the breakers. Then swim diagonally to shore. If you don’t know how to swim, stay out of the water!
Swim near a lifeguard.
Supervise children when in or near the water.
Respect the beach and water environment; know the water conditions.
Know your swimming abilities and limits.
Swim in groups.
Be aware of weather conditions; get out of the water and away from the beach during storms.
Stay calm in the event of an emergency.

Beach Flags:

Pay attention to beach warning flags and lifeguards.
RED flag means the surf is dangerous: stay out of the water;
YELLOW flag means use caution when entering the Gulf;
GREEN flag indicates waters are calm.
PURPLE flag means dangerous marine life may be present.
DOUBLE RED flags mean the water is closed to the public.