Omens today would be what most people call superstitions. This could include a black cat crossing your path, bad luck from breaking a mirror, etc.
What is sinful is to believe in an omen and act upon it. An example of this is to change direction after a black cat crosses your path. To feel a sense of dread when you see one, then this is not shirk.
“Seeking omens is shirk, seeking omens is shirk.” (Ahmad)
Ibn Mas’ood added, “There is none amongst us but feels something in his heart but Allaah can remove it through tawakkul.” (Tirmidhi).
This means that we should not act upon superstitions.
Optimism is a part of emaan, therefore anything that helps one to be optimistic is encouraged and is praiseworthy. A mu’min is always optimistic. Hope is a sign of emaan.
“No contagious disease and no omens, and I like al-fa’l (a good omen).” It was said, “And what is a good omen? He said, “A good phrase.” (Muslim)
This is a good sign you think is from Allah, and it must be optimistic. An example of this is making du’a to be blessed with something, and it’s a cloudy day, then you see the sun shining. A more obvious example is a good dream.
The Prophet (saw) would even seek good omens in people’s names. An example of this is in the incident at Hudaibiyah, when Suhail came, the Prophet (saw) said, “Now the matter has become easy.” (Bukhari)
This was a play on words of ‘Suhail’ and his saying Suhail has come to make things sahalah (easy).
By wearing talisman, you give the power of harm and benefit to something other than Allah when only Allah has that power. This is shirk in Ruboobiyyah. It is shirk in Uloohiyyah because you put your trust (tawakkul) into it.
Another example is after supplicating for rain, the Prophet (saw) turned his cloak inside out. This was a fa’il (good omen). They used to do this a symbol for signifying change – i.e. from drought to rain.
Ibn al-Qayyim also mentioned once that he lost his son during hajj and thought he had died or been kidnapped. Then he saw a people who became excited after finding a lost camel, so he took that as a good omen and then found his son.
In general, talismans and omens are shirk.
When a person uses a talisman or omen, they often put their tawakkul in other than Allah
Give powers of Ruboobiyyah to other than Allah
Major shirk occurs if they give the talisman complete power, and it is minor shirk if they think that Allah has given the taweez, for example, powers.