ΔH° is the change in enthalpy or heat -This exchange of heat or enthalpy takes place in system and surroundings.
A chemist views this change from the system - if heat is added to the system from surroundings  -ΔH°is positive and if heat is removed or released from the system to the surroundings -ΔH°is negative.

However a Physicists thinks in terms of the surroundings.-
if heat is added to the system from surroundings  -ΔH°is negative and if heat is removed or released from the system to the surroundings -ΔH°is positive.