Q: Is it correct that the ordinary sign of veneration of the altar (by the laity) is a profound bow? Is it recommended or permissible for laity to kiss the altar (as a sign of veneration outside the sacred liturgy) or is this reserved to the clergy alone during the liturgy?
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A: GIRM 275b says that a profound bow is made to the altar. It distinguishes from the genuflection made to a tabernacle. It would be in keeping with these distinctions if all Catholics used the proper reverences.
During mass, the priest and deacon alone kiss the altar. The servers do not. The reader does not. The communion minister does not.
The rubrics do not say much about what happens outside mass. Some people kiss icons and statues. I suppose they could kiss an altar. I just would not promote it because the profound bow seems to be what the church has in mind.