First, senior lecturer: this is an academic rank in the UK, Ireland, Commonwealth countries (e.g. Australia) and various other countries, but not in the US.

There is no single standard abbreviation, but the two most commonly found are Sen. Lec. and Snr Lec. Here are examples of each:

https://www.google.es/search?num=100&q="Sen. Lec."&oq="Sen. ...
https://www.google.es/search?num=100&q="Snr Lec."&oq="Snr Le...

Occasionally, the "lecturer" part is abbreviated as "Lctr", but the most common are the two mentioned above.

Note, by the way, that the rule on full points at the end of abbreviations nowadays, at least in the UK, is normally that you add a point when the abbreviation does NOT include the last letter of the word and you do not add a point when it does include the last letter (this is strictly a contraction rather than an abbreviation). So Sen. and Lec. have a final point but Snr does not.

As for "Doctor of Science", the Wikipedia page cited by Taña below says that Sc.D., D.Sc., S.D. or Dr.Sc. are all used in various places. Since the Senior Lecturer title suggests that this probably refers to the UK, the most common abbreviation by far is DSc. That's the abbreviation in Oxford, London and many other places. Cambridge, just to be different, uses ScD. Others are also found, but the standard by default is DSc.

In the UK it is customary nowadays not to include points in abbreviations of academic degrees, so BA, PhD and DSc are much more commonly used (at least in UK academic circles) than B.A., Ph.D. and D.Sc. This was not always so and on the whole it is not so in the US.

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Note added at 5 hrs (2013-08-28 12:02:13 GMT)
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This answer assumes that the person referred to occupies an academic position in and holds an academic degree from the UK or another country where these titles exist. If they are being used in a translation of the credentials of a person from another country, care is required. There's no harm in calling someone a "senior lecturer" if they hold an equivalent rank (such as the Croatian Viši predavač, for example -- the map in your profile suggests this may be relevant). But you should not really use an abbreviation like "DSc" without qualification unless the person actually holds a degree called "DSc". If the person holds an ordinary doctorate in a scientific subject, the equivalent is PhD. Doctor of Science (DSc) is a higher doctorate in the UK (that is to say, a doctorate occasionally awarded to people with a very distinguished research record who normally already hold a PhD or equivalent). This point should be checked carefully and the abbreviation DSc should certainly not be used unless the person has such a degree.

I suspect this is not the case, since it is fairly unusual for a Senior Lecturer to hold a DSc in the UK. Normally it would be awarded to people of professorial rank.

Depending on the context, it is usually necessary to add some kind of note in these cases, or to give the name of the original degree in the original language and add "equivalent to..." in parentheses.