Qiqi Abaziz's answer is ok, but I still struggled for a long time getting it to work with the compatibility pack and to apply the style to the correct elements. Also, the transparency-hack is unneccessary. So here is a complete example working for v8 and up:
values\styles.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="MyActivityTheme" parent="@style/Theme.AppCompat">
<item name="actionBarStyle">@style/NoLogoActionBar</item> <!-- pre-v11-compatibility -->
<item name="android:actionBarStyle">@style/NoLogoActionBar</item>
</style>
<style name="NoLogoActionBar" parent="@style/Widget.AppCompat.ActionBar">
<item name="displayOptions">showHome</item> <!-- pre-v11-compatibility -->
<item name="android:displayOptions">showHome</item>
</style>
</resources>
AndroidManifest.xml (shell)
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">
<uses-sdk android:minSdkVersion="8" android:targetSdkVersion="19"/>
<application android:theme="@android:style/Theme.Light.NoTitleBar">
<activity android:theme="@style/PentActivityTheme"/>
</application>
</manifest>