1. Backpack with a scallop shell:
The most obvious sign of a peregrino is the everpresent burden they carry with a scallop shell tied to it. Pilgrims on bikes have them on the bikepacks. Some pilgrims may even wear a shell around their neck.
Further along the way to Santiago, the pack size per pilgrim diminishes, sometimes into just a waistpack This variety of peregrino are usually those who begin walking from a closer point to Santiago. Besides the lack of a backpack, their clothes and pants and boots are especially fresh.
The "fresh" pilgrims also have a tendency to want to talk and have no concept of the "veteran" pilgrim who is on day 20+ and is a bit weathered both emotionally and physically. * (see Addendum 1: Pilgrim Etiquette)
2. Zipoff pants:
Pilgrims can be spotted sans backpack or gear by the fact that their pants zip off into shorts. Zip-offs are universal, non-country or culture specific, quite often khaki.
It is 99.99% correct to guess a person wearing these is/was walking the camino.
3. Walking sticks:
These range from the sport walking sticks that are store bought (like cross-country ski poles) to the traditional sheperd's stick (with a small gourd tied to the end of it.)
Some pilgrims opt to pick up a tree branch along the camino.
Unfortunately, peregrinos have a tendency to leave their walking sticks behind, much to the profit of many small Spanish villages. **(see Addendum 2: The Pilgrim Industry)
4. Boots & hat
Not too many peregrinos walk without a good pair of boots or hat. There's the odd one who sometimes choose to walk in their back-up sandals/flipflops (see #7), but almost every pilgrim will have the worn boot and hat to complete the pilgrim uniform.
5. The Camino tan/sunburn:
Many a peregrino can be seen sporting a burnt nose and uneven arm tans.
Due to the consistent migration of pilgrims towards Santiago in the West, the peregino's left forearm may get unearthly dark.
Depending on what is worn, & how much sunscreen is applied, a pilgrim will have blotches around the neck arms and legs, & possibly a raccoon tan on the face if wearing sunglasses.
For those peregrinos of alabaster skin, these same areas (and quite often more) can be lobster red.
6. The fleece (or in Canadian, the "flee-cee")
Most pilgrims carry the fleece jacket from closer to the beginning of the route due to unexpected cold weather in the mountains.
The fleece, also doubles as a blanket in a cold albergue (of which there are many.)
7. Sandals/flip-flops ('con' sock or 'sin' sock)
Most often used post-boot in the evenings, sandals also act a a foot guard for showers.
The sandal-fleece combination is also typical of the peregrino and many wear the sandals with socks for extra blister prevention.
8. The Peregrino Limp (© John & Gen):
Pilgrims can be spotted at the end of day waddling through the streets in their sandals and fleece with slow and deliberate steps to ease the pain from blisters and aching muscles.
The Peregrino Limp is especially accentuated when stairs are involved.
When & Where to Pilgrim Spot:
Pilgrims can be seen at every small village bar or café along the camino. Within larger cities, one cannot turn a corner without spotting the zipoff pants and fleece, and/or backpack with the scallop shell tied to it.
On a busy street near a particular city attraction, a hundred pilgrims can be seen milling around with locals & other tourists.
Other high pilgrim areas include restaurants/bars near albergues, pharmacies for foot care products, the one village grocery store, and anywhere there is internet.
*Addendum 1: Pilgrim Ettiquette
At the beginning of the camino, pilgrims could simply say "buen camino", and it was acknowledged that one would move on individually. But with the fresh, or sometimes the simply annoying, obnoxious peregrinos, a veteran (being much more fit, even if not so fresh) can boost ahead. Or, sometimes the veteran alternatively stops in his/her tracks and lets the disruptive pilgrim go on.
**Addendum 2: The Pilgrim Industry
Spanish villages may possibly make a fortune off of lost walking sticks & other items left along the camino.
In the past, it was said that many items were left roadside, particularly at the beginning of the camino. (i.e. leather jackets, enough books to fill a library.)
But pilgrim equipment is surprisingly absent from the camino roadsides today, and (thankfully) clear of debris & litter of any kind. Cow dung & horse poop are the exception.