Signifying a stoplight is new and not yet in service

[roadman65]

Florida bags them and flashes them for periods of one to three weeks (depending on the county).

[Dr Frankenstein]

Québec seems to have varying techniques. Sometimes they aim them down, sometimes they make them flash. I've never seen them bagged.

They also post a sign saying "SIGNALS IN SERVICE <date>", in French, at the intersection approach.

They also have a "SIGNALS REMOVED <date>" variant, as well as ones for stops and speed limits.

[US71]

Québec seems to have varying techniques. Sometimes they aim them down, sometimes they make them flash. I've never seen them bagged.

They also post a sign saying "SIGNALS IN SERVICE <date>", in French, at the intersection approach.

They also have a "SIGNALS REMOVED <date>" variant, as well as ones for stops and speed limits.

I've seen "Signals Removed" once or twice in my travels.

Sometimes, if a signal is new, I've seen flags on the Signal Ahead signs (also used for new STOPs, Bus Stops and Speed Limits)

[roadman65]

Orange County, FL uses a portable VMS to place at a new signal instalation.  The flags on a signal ahead signs were used at locations where flashing beacons became full signals, now this seems to be the way for all.

SC uses signal ahead signs with a "NEW" panel attached.

[xcellntbuy]

Most of the new mast-arm signals being installed in Broward County, Florida are pointed down to the roadway until they become operational.

[apeman33]

Basically, I can say I've seen every variant listed here used in Kansas (excluding the Quebec signs in any language). There doesn't seem to be a SOP for new signals. The most common seems to be to bag them, then have a flashing stage before going to a regular cycle.

[txstateends]

I've seen mixed treatments here in TX also.  Some places bag them with burlap, others use plastic.  Some turn them down, others up.  Some places use a flashing-yellow preview, others seem to fully activate them after the unveiling or straighening.  A few give you warning ahead of time with upright-angled flags above the "signal ahead" signs if the light is new.