Like most of you, I do have my own experience and my own perspectives so this is my shared thoughts about the tattoos.
First, I consider tattoos to be symbols with deep meaning because tattoos (permanent ones) don't wash after the first rain or shower so there's the time factor to them... when I bring time into equation I say portals, always.... time = portals therefore, a tattoo becomes a portal with a specific meaning, energy and symbiology.
I've studied a few things about tattoos especially body art with deep meaning like tribal tattoos, Yakuza, indigenous, meanings, positions on body parts and all carry information and meaning on top of the actual visual representation of the tattoo.
As far as sigils as tattoo ... and charging a sigil via pain and blood... it depends... because I would not charge a sigil with pain unless the manifestation of the sigil is to generate pain.
Blood magic is less understood by practitioners because of the commodity and lines becomes blur and magic diluted because it is possible.
A few examples.
Some female practitioners use menstrual blood in their magic with strong belief it will help in whatever crafts and spells but it is not that simple.
Menstrual blood is considered "dead blood" because it is no longer needed by a living body, therefore... eliminated.
Pure blood - potent and pure blood is found in the neck zone, the side where heart is (vampires knew

) because that blood is highly oxygenated* for the brain use.
Heavy blood - not so good in some magic practices is the blood from the lower part of the body.. feet... varicose veins, heavy metals, thicker blood....
I hate it when it happens... I start with an idea and being flooded by so many downloads all at once....and not in a specific order....
About oxygenated blood... we need oxygen for our optimal survival.
Imagine we breathe in consciousness. Low levels of oxygen in blood generate hypoxia and cerebral aneurysms.
If you hold your breath for a long time, not the lungs will be the main problem but you will loose consciousness first.
So back to sigils as tattoos... I would not recommend unless determined to carry that portal for a long time.
I would not suggest charging sigils with pain unless pain is the main manifestation of the sigil otherwise, use a crystal to convert pain into a more useful energy to charge the sigil.
Definitely not suggesting blood for charging and activating sigils because of the above mentioned reasons.
Of course there are exceptions and one can choose whatever they think it is working for them reality is created by using belief as building blocks so... use the right tools for the right reasons expecting a specific outcome.