C00E: 86 08        LDA #$08    Set A = 8
C010: B7 27 00     STA $2700   Store 8 in $2700

Via experimentation with the debugger, we can observe that the value at $2700 appears to be set to:

• 8 when we start/reset the machine and load the start screen
• 1 when the user starts a game with skill level 1 (easiest)
• 2 when the user starts a game with skill level 2
• 3 when the user starts a game with skill level 3
• 4 when the user starts a game with skill level 4
• 5 when the user starts a game with skill level 5
• 6 when the user starts a game with skill level 6
• 7 when the user starts a game with skill level 7
• 8 when the user starts a game with skill level 8 (hardest)

It's fairly obvious, then, that the variable at $2700 indicates the skill level. Most likely we initialize it to 8, the hardest skill level, so that the aliens running in "demo mode" on the start screen are plentiful and aggressive.