Possible to make the Vin pin on my UNO transmit data?

I need 12V to actuate a solenoid actuator I'm using for a project, and the only place I know where to get 12V on my UNO is through the Vin pin when I have it connected to a 12V power supply. Is that assumption correct? How could I turn the Vin pin into a pin that I can use to actuate the solenoid?

You don’t, you connect the 12v to the solenoid and turn it on/off with a digital pin and a transistor or other device that can handle the solenoid current.

Look for examples of driving a relay, that’s the same thing.

Arduino Uno doc say you can get the unregulated external volts or supply them through the VIN pin.

Vin. The input voltage to the Arduino/Genuino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.

whereas the 5V pin is not regulated.

5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

Connect 12V through the power plug then measure voltage between VIN in GND for 12V and then between 5V and GND for 5V. If both are true then question is how many mA of 12V you can use.

There is a 1A rated diode between the barrel jack and the Vin pin.
I would not supply solenoid coil power from Vin. Instead, connect it in parallel with the feed to the barrel jack, and use an Arduino-controlled transistor to sink the solenoid current as previously advised.

So the real answer is that it's a power issue.

My guess is that there are tiny (toy) solenoids that would be safe but if you don't want to get smoke, do as the Engineers tell you, the practice will have you ready for bigger things.

Would this be a suitable circuit?

I can’t open that (proxy error). Is it the same as this?
(also shows as LED to indicate On)

I was able to open it and the circuit shown does everything that Crossroads advises AGAINST. All solenoid power is drawn through the Arduino Vin pin.

Is this the valve?

We tried this solenoid at various DC voltages and found we could actuate it down at 6VDC (although it was a little slower to open). Here is the current draw table for various voltages. We suggest a TIP120 or N-Channel power FET with a 1N4001 kickback diode to drive this from a microcontroller pin. For a power supply, our 9V 1A or 12V 1A power adapters will do the job.

If you want a beefier water valve, we also carry a brass version which does not have a minimum pressure requirement and can be used with liquid flow in either direction.

Voltage Current
6V 160 mA
7V 190 mA
8V 220 mA
9V 240 mA
10V 270 mA
11V 300 mA
12V 320 mA

I'm fairly certain this is the actuator I have.

It looks a lot like this.

To drive a solenoid you will need a power transistor and a diode, check this diagram for how to wire it to an Arduino or other microcontroller. You will need a fairly good power supply to drive a solenoid, as a lot of current will rush into the solenoid to charge up the electro-magnet, about 100mA, so don't try to power it with a 9V battery!

There's a link embedded on the Adafruit site in there but PDF's lock my XP/PC up so I can't link it.

Looking on eBay I see these specs:

DC Solenoid Electromagnet

Model: JF-0530B
Rated Voltage: DC 12V
Type: Pull Push
Rated Current: 300 mA
Force&Stroke: 5 N/10 mm