There are numerous observances which we have to remember that the Beis Hamikdash has still not been rebuilt.

These include:

At a Chasuna (wedding) we (discreetly) place ash on the Chasan’s head in fulfillment of the verse that we should remember Jerusalem even at the time of our greatest joy.

Likewise, at a Chasuna,  when the Chupah ceremony is completed, we have the Chassan break a glass to remember the loss of the Beis Hamikdash.

 

When a person sees the place of the ruins of the Beis Hamikdash, they should recite “Boruch Dayan Hoemes” (Blessed in the true judge), without saying Hashem’s Name as we do by current mourning of a passed relative. Then, while standing, they should tear the garment that they are wearing.