Well, I was downloading some How To's. A big folder of them actually, nothing magick related as far as I could tell. But I was surprised to see a 'Magick' folder with a few text's in. But one caught my eye. It's a list of sigils for summoning (individual) demons, I can't verify that they're real though, so I was asking here.
It seems legit enough, there is even a large warning at the bottom for these to be only used in times of extreme emergency.
I will only give the image to those who are known as trustworthy on the site. If they are real I don't want people to abuse them, because some of these are 'evil' summoning sigils and I know many people want to go about summoning things.
It may be that you've stumbled upon an amateur copy of the Goetia.. You might do a google image search of Goetic Sigils and see if those are what you saw..
None of the symbols match, but I did make a discovery with the last one. The demon/spirits names are in the book, but none of the sigils match. I did find a discussion board for this image, and someone said many of these are wrongly drawn or don't match the correct demons/spirits.
Usually, if you come across sigils like that, they were taken from the goetia like whiteraven said. If not, you could check it's sequel the theurgia goetia, the grimoireum verum, the black raven, or the grimoire of armadel. Did the sigils look like lines with a circle one one end and a perpendicular one on the other. If so, then they were made useing the rose cross.
"I did find a discussion board for this image, and someone said many of these are wrongly drawn or don't match the correct demons/spirits."
You just described the grimoire of armadel.
http://www.hermetics.org/pdf/grimoire/grimoireofarmadel.pdf
Most of the sigils are screwed up for example look at the red sigil of Zadkiel, then look at the sigil for Bethor in the Arbatel of magic. They're the same. Same thing for the sigils of Aratron and another sigil of Zadkiel. That brings up another point in the fact that the grimoire has 2-4 sigils for some spirits makeing it very confusing.