The following is a sample signature attack definition:
<Entry>
<Name>sample-sig</Name>
<Severity>Major</Severity>
<Attacks><Attack>
<TimeBinding><Count>2</Count>
<Scope>dst</Scope></TimeBinding>
<Application>FTP</Application>
<Type>signature</Type>
<Context>packet</Context>
<Negate>true</Negate>
<Flow>Control</Flow>
<Direction>any</Direction>
<Headers><Protocol><Name>ip</Name>
<Field><Name>ttl</Name>
<Match>==</Match><Value>128</Value></Field>
</Protocol><Name>tcp</Name>
<Field><Name><Match><</Match>
<value>1500</Value>
</Field></Protocol></Headers>
</Attack></Attacks>
</Entry>