They only speak that in their blindness and ignorance.
[2Th 2:11-12
11 And for this reason God will send them strong delusion, that they should believe the lie,
12 that they all may be condemned who did not believe the truth but had pleasure in unrighteousness.
'Re-united with Mum', 'Resting in Peace', 'Looking down on us'. These are the kind of sentiments expressed in many death notices. How can any atheist express such sentiments with an ounce of certainty or credibility?