User blog comment:Aftenshnoshnikr/Summon Sign Locations/@comment-5974459-20130713220633

the beggining of each area is usually a place to put down summon signs, you might also find a few signs right before the fog door of each boss, you must be in soul form to use a blue eye stone and in human form to summon phantoms...

The game is quite empty nowadays compared to DaS, but there is a bigger chance to find people playing in nighttime (that is, if you live in the USA)