Stig

For a static subject in steady light they genuinely produce the same picture, which is why your test showed nothing. The differences appear in specific conditions.

Electronic shutter advantages:

• Silent. No moving parts, no sound at all. This is transformative for theatre, ceremonies, wildlife and anywhere a click is intrusive.
• No vibration. Nothing moves, so there is no shutter shock softening long-lens or macro shots.
• Very fast top speeds and high burst rates.
• No mechanical wear. Mechanical shutters have a rated life measured in actuations.

Electronic shutter problems, and these are the ones that catch people:

• Rolling shutter distortion. The sensor is read out line by line rather than all at once, so anything moving fast across the frame is skewed. Propellers bend, golf clubs curve, a panned car leans.
• Banding under artificial light. Many light sources flicker, and reading the sensor progressively records different brightness on different lines. You get horizontal stripes.
• Flash is usually unavailable or severely limited.

One practical footnote: the silent mode is silent enough that people around you do not know you are shooting, and that is worth thinking about beyond the technical question.

In some settings — ceremonies, performances — that is exactly the point and it is a courtesy. In others, being visibly and audibly a photographer is what makes people comfortable, and a camera that gives no signal it is working can read as sneaky.

Several cameras offer a synthetic shutter sound for this reason, which sounds absurd and is genuinely useful.

One safety point in the other direction, since the concern is people worrying unnecessarily: it is worth telling somebody where she is going and roughly when she will be back.

Lying still in remote places, often at dawn or dusk, alone, is a genuine risk profile even though the specific alarm in this thread is a false one. The nice irony is that the same signals that stop strangers worrying — visible equipment, bright clothing — also make her easier to find if anything ever does go wrong.

There is no established signal, which is a genuine shame — other activities have one. Divers have a recognised flag meaning there is somebody in the water, and the whole point is that it is understood without explanation.

Photography has nothing equivalent, so the practical answers are all improvised. The ones that work in ascending order of effort:

Be visibly equipped. A tripod standing beside her, a camera bag open, a lens cap on the ground. People read a scene, and equipment scattered around a prone person changes the reading from emergency to activity almost instantly. A tripod is the single most effective object because it is unmistakable at distance.

High-visibility clothing. Counter-intuitive for landscape work, but a bright vest reads as "working" rather than "collapsed" from a long way off.

Move occasionally. A small deliberate movement every so often is enough to stop most people approaching.

The K is worth explaining separately since it is the part that looks like an inconsistency.

In theory, full cyan plus magenta plus yellow absorbs everything and gives black. In practice it gives a muddy dark brown, because real inks are not perfect absorbers.

So a dedicated black ink is added, and it does four jobs: proper blacks, cleaner neutral greys, sharper black text, and a lot less ink on the page — laying down three saturated inks everywhere something is dark soaks the paper and costs three times as much.

That is a good illustration of the general pattern: the theory says three inks suffice, and the materials say otherwise. It is also why many photo printers use more than four inks — extra light cyan, light magenta, greys and sometimes orange or green — each one added to fix a specific place where the four-ink model falls short.