On 2013–04–10 Tristan Lorino wrote:

> I'm beginning with ConTeXt.

You probably compiled your document with texexec. That means you are
using an old, but still supported, version of ConTeXt called MkII.
You can make you life easier if you use the newer version MkIV
instead. Just compile with

  context somefile.tex

instead of texexec. And you can skip the \enableregime line.

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> […]
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> 
> How can I avoid these symbols?

If you use MkIV, those symbols don't show up. I don't know why they
are visible with MkII.

Marco