Blinkage

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According to the California driver handbook,

Before changing lanes, signal, look in all your mirrors, and:

• Check traffic behind and beside you.
• Glance over your left or right shoulder to make sure the lane you want is clear.
• Look for vehicles or motorcyclists in your blind spot.
• Be sure there is enough room for your vehicle in the next lane.

No mention of signals. But if you consider changing lanes a turn, here's the law:

CVC 21703

Proper Use of a Turn Signal

22108. Any signal of intention to turn right or left shall be given continuously during the last 100 feet traveled by the vehicle before turning.

Which would be both a request and an alert, making this bumper sticker unnecessary: