HOMER's "findPeaks" tool will accept input from sequencing runs that are strand-specific. This is why the value is included in the file specifications. But the default when calling peaks is to use "BOTH", which can be interpreted as all peak calls being unstranded (merged). HOMER interprets these as a strand assignment of "0" (translates to +).
In BED files, a dot "." can be used successfully with many tools to represent a "NULL" value for strand (this defaults to "+" when used with some tools). I would give this a try first, but I am not certain if it will work since I haven't tried it. So give it a test. If it doesn't work, just use "+" for all entries in your BED file.
When converting BED to a Peak file (using the tool provided in the HOMER tool suite), the "+" will be converted to "0". This is a good idea to do, since some of the tools in this package only work with strand annotated with "0" or "1". The start coordinate value will also be modified to have a 1-based start, instead of the 0-based start used in BED format.
To my knowledge, stand will not even be considered by many of the functions in HOMER, so I wouldn't worry too much about setting this value to "+" or "0"