How does a Muslim perceive Laylat al-Qadr and become certain of it?

Allah singles out some of His servants by apprising them of a sign for Laylat al-Qadr, such as seeing a dream in their sleep or observing a change in cosmic phenomena, leading them to be certain or to strongly believe that it is Laylat al-Qadr, as happened to some Companions and Ubayy ibn Ka'b.