I am trying to get the meaning of the symbol ‡. I saw it a couple of times: as a tattoo in a little boy finger, and on Wikipedia.
How is this symbol called in English?
It is a double dagger and it is often used in typography to indicate a footnote.
The simple one (†), with only one horizontal bar is called a dagger after it's resemblance with the blade.
If you have two footnotes on a given page, the first one will be marked with the single dagger and the second one with the double dagger.
In lists of peoples (authors, military staff), the dagger will indicate a dead individual.
In tattoos, the dagger (e.g. on the arm) will sometimes mean that the bearer has had a military past or is not afraid of death.
Considering that St Nicholas is the patron Saint in charge of orphans (among other duties), it would mean that the young boy is asking for some heavenly protection for want of a better earthly one.
It is a “double dagger” (Unicode character U+2021). It is a variant of the “dagger” (also called “obelus”) character (†).
Wikipedia has an extensive list of possible uses in typography, but it is mostly used to introduce footnotes. Typically, the first footnote is introduced with an asterisk (*), the second one with a dagger, and the third one a double dagger.