Try it this way:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" encoding="utf-8" />
<xsl:template match="/">
<xsl:for-each select="data/sig">
<xsl:call-template name="tokenize">
<xsl:with-param name="text" select="translate(., '-', ' ')"/>
</xsl:call-template>
<xsl:if test="position()!=last()">
<xsl:text> </xsl:text>
</xsl:if>
</xsl:for-each>
</xsl:template>
<xsl:template name="tokenize">
<xsl:param name="text"/>
<xsl:param name="delimiter" select="' '"/>
<xsl:variable name="token" select="substring-before(concat($text, $delimiter), $delimiter)" />
<xsl:if test="$token = translate($token, translate($token, '0123456789', ''), '')">
<xsl:value-of select="$token"/>
<xsl:text> </xsl:text>
</xsl:if>
<xsl:if test="contains($text, $delimiter)">
<!-- recursive call -->
<xsl:call-template name="tokenize">
<xsl:with-param name="text" select="substring-after($text, $delimiter)"/>
</xsl:call-template>
</xsl:if>
</xsl:template>
</xsl:stylesheet>
Note:
If you have multiple delimiters, you need to translate them to a common character (space in my example);
I didn't bother to remove the trailing space in each line;
If your processor supports the EXSLT str:tokenize() function, this could be simpler.