Here is the full list of all 16 HellSign achievements.
The base game contains 12 achievements, and there is 1 DLC pack containing 4 achievements.
DIED FOR THE FIRST TIME
DECIPHERED IDENTITY OF AN ENEMY
KILLED A BIRD
FOUND A RARE CLUE
AMPUTATED A HOMELESS GUYS ARM
FOUND CLUE WITH THERMAL DETECTOR
DEFEATED A SHADOW BOSS
DEFEATED A BANSHEE BOSS
DEFEATED A KELPIE BOSS
SUMMONED MOTHER BIRD!
FOUND CLUE WITH PARABOLIC MIC
KILLED A GHOUL
DEFEATED A LAMIA BOSS
DEFEATED A SKOLEX BOSS
DEFEATED A HARIONAGO BOSS
DEFEATED A EFREET BOSS