They are anything have no rule in Islam. Your hadith says "so seek not after them" and this question seems is seeking after them. They are permitted and so better we do not seek them.
As an example:
And [recall] when Moses said to his people, "Indeed, Allah commands
you to slaughter a cow." They said, "Do you take us in ridicule?" He
said, "I seek refuge in Allah from being among the ignorant." (67)
They said, "Call upon your Lord to make clear to us what it is."
[Moses] said, "[Allah] says, 'It is a cow which is neither old nor
virgin, but median between that,' so do what you are commanded." (68)
They said, "Call upon your Lord to show us what is her color." He
said, "He says, 'It is a yellow cow, bright in color - pleasing to the
observers.' " (69) They said, "Call upon your Lord to make clear to us
what it is. Indeed, [all] cows look alike to us. And indeed we, if
Allah wills, will be guided." (70) He said, "He says, 'It is a cow
neither trained to plow the earth nor to irrigate the field, one free
from fault with no spot upon her.' " They said, "Now you have come
with the truth." So they slaughtered her, but they could hardly do it. http://tanzil.net/#2:70
It is said in stories of prophets that there was only one cow with these specific terms. And it was for a young man who his father had a shop in market and his father was resting at noon and the key of shop was under his head while sleeping. At noon some very good customers came to home of young man and asked to immediately come and open the shop. When he came to pick the key see his father is sleeping and so did not want to bother his father and returned and said the customers I cannot open the shop and they left. For reward God sent those who were seeking to buy cow of this young man. After seek they found out only this young man has such a cow described by God. And young man said I sell it only if you give me gold at the same weight of cow. They finally accepted and young man became rich.
Another example is celebrating birthday of prophet that there is no evidence it is Haram in Islam. And so by default it is permitted.