s/ means "sobre", as Emiliano said at the beginning. It expresses the subject of the case in question. You can put "re:" or "regarding" or "in the matter of", as you prefer.

Some previous questions with "s/" in this sense:
http://www.proz.com/kudoz/spanish_to_english/law_general/503...
http://www.proz.com/kudoz/spanish_to_english/law_general/305...
http://www.proz.com/kudoz/spanish_to_english/law_general/526...

Without knowing what the case is about it's impossible to be totally sure about "procesamiento". If it were "procesamiento de desechos" it would be "processing". But that's pretty unlikely! Argentine cases labelled "s/ procesamiento" are nearly always appeals against indictment, or against some aspect of indictment, which, as Sandro has just said in the discussion, is the basic meaning of the word (that's how Tom West III translates it in his dictionary, for example):

"procesamiento
1. m. Acto de procesar.
2. m. Der. Acto por el cual se declara a alguien como presunto autor de unos hechos delictivos a efectos de abrir contra él un proceso penal."
http://lema.rae.es/drae/?val=procesamiento

"procesar
[...]
2. tr. Der. Declarar y tratar a alguien como presunto reo de delito."
http://lema.rae.es/drae/?val=procesar

"An indictment [...] in the common law system, is a formal accusation that a person has committed a crime. [...]
In England and Wales (except in private prosecutions by individuals) an indictment is issued by the public prosecutor (in most cases this will be the Crown Prosecution Service) on behalf of the Crown"
http://en.wikipedia.org/wiki/Indictment

Here's one Argentine among many "sobre procesamiento":
http://www.pjn.gov.ar/02_Central/ViewDoc.Asp?Doc=45696&CI=IN...

I think that without further information this is probably how you will have to translate it.

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Note added at 12 hrs (2013-11-07 07:26:04 GMT)
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As has been pointed out in the discussion, in order to refine the answer we really need to know the nature of the case, and the most suitable term may depend on whether British or American English is required. I offer "indictment" as a reasonable default option in the absence of further details. I also considered "prosecution". The Argentine cases are of the kind that would probably be heard in a higher criminal court in the UK (drugs, in many cases). They involve appeals against some aspect of the criminal proceedings to which the appellant has been subjected. I think "indictment" would serve as a general term covering this.