I can't find an example of "condamnation de police" in Belgium to confirm this, but I'm pretty sure it must refer to a condamnation or conviction is a tribunal de police, the lowest tier in the Belgian criminal justice system.

"Belgium has five first instance courts: Justices of the Peace, Police Courts, Courts of First Instance, Commercial Courts and Labor Courts. "
https://www.academia.edu/8942235/Belgiums_New_Specialized_Ju...

"The lowest level in civil and criminal matters consists of the Justice of the Peace Courts in civil matters and the Police Court in criminal matters. Apart from minor offences, the Police Court hears all cases involving traffic accidents."
http://www.iatj.net/congresses/Belgium.pdf (p. 2)

"Jugement
Un jugement est une décision rendue par un tribunal (tribunal de police ou tribunal correctionnel)."
http://www.policedegaume.be/Documents clients/doc/condamne.p...

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Note added at 1 hr (2016-01-27 10:22:37 GMT)
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Sorry: I meant "a 'condamnation' or conviction IN a 'tribunal de police'".

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Note added at 2 hrs (2016-01-27 12:11:14 GMT)
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Nikki's findings cast a different light on this, and it seems that "condamnation de police" refers to a conviction for which a "peine de police" was imposed. Whether this necessarily means that it was imposed in a police court I'm not sure, but I doubt it. There are sources that refer to it by a straight calque: "police sentence", "police penalty" or "police conviction", as in this article by a Belgian criminologist:

"Currently, 19 types of information are recorded, for each person, on the central judicial record, ranging from convictions (definitive) for a criminal, correctional or police sentence (including suspended ones) [...]
The decree of August 8, 1997, concerning the criminal record supposes that convictions for police penalties are erased after a period of three years after the date of the conviction. Certain police convictions nevertheless cannot be erased."
http://reflexions.ulg.ac.be/cms/c_36047/en/the-saga-of-the-c...

However, I really wouldn't advise this, at least without an explanation, because "police" makes it sound like a summary non-judicial penalty imposed by the police, like an on-the-spot fine, which is not the case.

I think the obvious translation is "minor convictions", possibly with some sort of explanatory note, possibly even with the original French term and the translation in parentheses.