I'm trying to find a translation, but it seems to be so informal that it doesn't appear properly in dictionaries.
The context would be like:
A: Do you know Hans? B: The new guy? A sends a picture B: Achso A: Siehste mal?
closed as unclear what you're asking by Em1, lejonet, fifaltra, Wrzlprmft♦, Vogel612 Jan 24 '14 at 6:45
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Siehste mal, which is the colloquial short reduction of Siehst du einmal, can have different meanings depending on the situation context. Here we have
The reaction of A as one wants to translate is not very logical because B has already had a look at it, and this question actually comes too late:
Better appropriate would be an exclamation mark (if that was just a typo?) and the meaning would turn into:
or, without question tag, it could mean a very colloquial short form of:
The word mal (which means einmal) is the time aspect and emphases this moment.
A more credible conversation would be: